Spread spectrum frequency synthesizer

ABSTRACT

A frequency synthesizer is described illustrating a method for modulation having an adjustable standard curve used to modulate an input signal for spread spectrum modulation. In particular, the a standard curve is generated, wherein the standard curve modulates an input signal to generate a spread spectrum of frequencies. The standard curve is associated with a standard modulation frequency. The standard curve is sampled at a constant sampling frequency. A shape of the standard curve is adjusted, such that critical points of the standard curve are captured when sampling the standard curve. The shape of said standard curve that is altered varies between at least two periods.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation in part and claims the benefit of andis related to U.S. patent application Ser. No. 11/172,691 by Shuliang Lifiled on Jun. 30, 2005 now U.S. Pat. No. 7,405,629 “FREQUENCY MODULATORCIRCUIT AND METHOD THAT USES MULTIPLE VECTOR ACCUMULATION TO ACHIEVEFRACTIONAL-N FREQUENCY SYNTHESIS”, all of which are assigned to theassignee of the present invention, which are incorporated herein byreference.

TECHNICAL FIELD

Embodiments of the present invention relate to electronic technologies.More specifically, embodiments of the present invention are related to aphase lock loop control system and method.

BACKGROUND

The following descriptions are not admitted to be prior art by virtue oftheir inclusion in this section.

Electronic systems and circuits have made a significant contributiontowards the advancement of modern society and are utilized in a numberof applications to achieve advantageous results. Numerous electronictechnologies such as digital computers, calculators, audio devices,video equipment, and telephone systems facilitate increased productivityand cost reduction in analyzing and communicating data, ideas and trendsin most areas of business, science, education and entertainment.However, the electronic systems that provide these advantageous resultstypically emit electromagnetic signals. These electronic systems arealso often operated in close physical proximity to other electronicsystems and interfere with the operations of the other electronicsystems. However, traditional attempts at mitigating electronicemissions are often expensive and relatively resource intensive.

A number of electronic systems include phase lock loops can be utilizedin attempts to perform a variety of functions. For example, some phaselock loops are utilized in frequency synthesis. In a frequencysynthesizer, a phase locked loop (PLL) is usually used tomultiply/divide the frequency of a selected low frequency crystal. ThePLL is used to force the frequency of a voltage controlled oscillator(VCO) output to change until a feedback loop frequency and an inputfrequency to a phase detector have a particular phase relationship.Controlling the output of the phase lock loop can be complicated and/orinvolve a relatively significant amount of circuit resources.

SUMMARY OF THE INVENTION

A frequency synthesizer is described illustrating a method formodulation having an adjustable standard curve used to modulate an inputsignal for spread spectrum modulation. In particular, the a standardcurve is generated, wherein the standard curve modulates an input signalto generate a spread spectrum of frequencies. The standard curve isassociated with a standard modulation frequency. The standard curve issampled at a constant sampling frequency. A shape of the standard curveis adjusted, such that critical points of the standard curve arecaptured when sampling the standard curve. The shape of said standardcurve that is altered varies between at least two periods.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiments of the present invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1A is a block diagram of an exemplary modulation frequencysynthesizer in accordance with one embodiment of the present invention.

FIG. 1B is a block diagram of an exemplary modulation phase-locked loop(PLL) frequency synthesizer, in accordance with one embodiment of thepresent invention.

FIG. 1C is an exemplary architecture diagram of an exemplary modulationcontrol pattern generator feedback loop in accordance with oneembodiment of the present invention.

FIG. 2 is a block diagram of an exemplary phase lock loop controller inaccordance with one embodiment of the present invention.

FIG. 3A is a block diagram of an exemplary frequency spreading controlpattern generation system in accordance with one embodiment of thepresent invention.

FIG. 3B is a diagram of three error vectors extending from an average Pvalue derived from a P pattern sequence and used in determining thefractional-N value, in accordance with one embodiment of the presentinvention.

FIG. 3C a diagram showing an exemplary graphical representation of threeerror correction vectors in accordance with one embodiment of thepresent invention.

FIG. 4 is a flow chart of an exemplary frequency spreading controlpatter generation method, in accordance with one embodiment of thepresent invention.

FIG. 5A is a block diagram of an exemplary cross zero best errorselection system in accordance with one embodiment of the presentinvention.

FIG. 5B is a block diagram of an exemplary implementation of frequencyspreading control pattern generation system utilizing a cross zero besterror selection system in accordance with one embodiment of the presentinvention.

FIG. 6 is a flow chart of an exemplary cross zero best error selectionmethod in accordance with one embodiment of the present invention.

FIG. 7 is a block diagram of a spread spectrum modulator that is capableof enhanced noise shaping, in accordance with one embodiment of thepresent invention.

FIG. 8A is a block diagram of the noise shaping modulator of FIG. 8, inaccordance with one embodiment of the present invention.

FIG. 8B is a block diagram of the noise shaping modulator of FIG. 8, inaccordance with one embodiment of the present invention.

FIG. 9 is a flow chart in a method for producing a signal of selectablefrequency with enhanced noise shaping, in accordance with one embodimentof the present invention.

FIG. 10A is a diagram of a frequency response of the output frequencyfrom a frequency synthesizer without any noise enhancements, inaccordance with one embodiment of the present invention.

FIG. 10B is a diagram of the frequency response of a frequencysynthesizer with noise enhancements of the present invention.

FIG. 11A is a block diagram of a spread spectrum frequency synthesizerincluding a first order accumulator for generating a linear standardcurve, in accordance with one embodiment of the present invention.

FIG. 11B is a block diagram of a spread spectrum frequency synthesizerincluding a first order accumulator for generating a non-linear standardcurve, in accordance with one embodiment of the present invention.

FIG. 12A is a flow chart illustrating steps in a method for generating astandard curve that modulates a PLL to generate a spread spectrumfrequency profile, in accordance with one embodiment of the presentinvention.

FIG. 12B is a flow diagram illustrating steps in a method for generatinga standard curve from the plurality of input signals, in accordance withone embodiment of the present invention.

FIG. 13A is a block diagram of a spread spectrum frequency synthesizerincluding a higher order accumulator block for generating a non-linearstandard curve, in accordance with one embodiment of the presentinvention.

FIG. 13B is a block diagram of the higher order accumulator block ofFIG. 13A comprising a plurality of accumulators coupled in series forgenerating a non-linear standard curve that is modulated to generate afrequency profile, in accordance with one embodiment of the presentinvention.

FIG. 13C is a block diagram of the higher order accumulator block ofFIG. 13A that sums a non-linear curve and a linear curve for generatinga non-linear standard curve that is modulated to generate a frequencyprofile, in accordance with one embodiment of the present invention.

FIG. 13D is block diagram of an accumulator used in the higher orderaccumulator block of FIG. 13A, in accordance with one embodiment of thepresent invention.

FIG. 14 is a flow diagram illustrating steps in a computer implementedmethod for generating a non-linear standard curve that is modulated togenerate a spread spectrum frequency profile, in accordance with oneembodiment of the present invention.

FIG. 15 is a diagram of a standard non-linear curve, in accordance withone embodiment of the present invention.

FIG. 16 is a flow diagram illustrating steps in a computer implementedmethod for modulating a standard curve in a spread spectrum modulatorsuch that peaks of the standard curve are captured, in accordance withone embodiment of the present invention.

FIG. 17 is a flow diagram illustrating steps in a computer implementedmethod for modulating a standard curve in a spread spectrum modulatorsuch that a length of the standard curve comprises an integer thatcaptures peaks of the standard curve depending on the shape of thestandard curve, in accordance with one embodiment of the presentinvention.

FIG. 18A is a graph illustrating the manipulation of the length of thestandard curve in order to improve EMI reduction, where the length is20, in accordance with one embodiment of the present invention.

FIG. 18B is a graph illustrating the poor sampling of the standard curveduring modulation when the length is 21, in accordance with oneembodiment of the present invention.

FIG. 18C is a graph illustrating the poor sampling of the standard curveduring modulation when the length is 22, in accordance with oneembodiment of the present invention.

FIG. 18D is a graph illustrating the poor sampling of the standard curveduring modulation when the length is 23, in accordance with oneembodiment of the present invention.

FIG. 18E is a graph illustrating the manipulation of the length of thestandard curve, where the length is 20 and 24, in accordance with oneembodiment of the present invention.

FIG. 19A is a flow diagram illustrating a computer implemented methodfor adjusting a shape of a standard curve in a spread spectrummodulator, in accordance with one embodiment of the present invention.

FIG. 19B is a flow diagram 1900B illustrating a computer implementedmethod for sampling a linear curve, in accordance with one embodiment ofthe present invention.

FIG. 19C is a flow diagram 1900C illustrating a computer implementedmethod for sampling a non-linear curve, in accordance with oneembodiment of the present invention.

FIG. 20A is a graph illustrating the manipulation of periods within anon-linear standard curve in order to improve EMI reduction, inaccordance with one embodiment of the present invention.

FIG. 20B is a graph illustrating the manipulation of periods within alinear standard curve in order to improve EMI reduction, in accordancewith one embodiment of the present invention.

FIG. 21A is a block diagram of an exemplary phase lock loop controllerin accordance with one embodiment of the present invention.

FIG. 21B is a flow chart of an exemplary feedback loop divider controlvalue adjustment method in accordance with one embodiment of the presentinvention.

FIG. 21C is a block diagram of exemplary feedback loop divider controlvalues in accordance with one embodiment of the present invention.

FIG. 22 is a flow chart of an exemplary simplified spread spectrummodulation pattern generation method in accordance with one embodimentof the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the embodiments of the presentinvention, systems and methods for modulating a phase lock loop (PLL)signal. While the invention will be described in conjunction with theembodiments, it will be understood that they are not intended to limitthe invention to these embodiments. Furthermore, in the followingdetailed description of the present invention, numerous specific detailsare set forth in order to provide a thorough understanding of thepresent invention. However, it will be recognized by one of ordinaryskill in the art that the present invention may be practiced withoutthese specific details. In other instances, well known methods,procedures, components, and circuits have not been described in detailas not to unnecessarily obscure aspects of the present invention.

Present invention phase-locked loop control systems and methodsfacilitate control of phase-lock loop operations. In one embodiment,phase-lock loop control systems and methods are utilized in theimplementation of a modulated frequency synthesizer for facilitatingefficient frequency spreading over a designated spectrum. It isappreciated that present invention embodiments can have a variety ofimplementations and can be compatible with vector accumulation. Forexample, a phase-locked loop control system or method can facilitategeneration of a variety of modulation patterns, including but notnecessarily limited to linear or non-linear modulation, standard ornon-standard modulation, etc.

Accordingly, embodiments of the present invention facilitate generationof modulated signals. The modulation can be performed on the fly and canbe scalable permitting multiple modulated patterns to be achieved (e.g.,a variety of frequency spreads, a variety of fractional divisions, etc).The generation of multiple modulated signals is relatively fast and canbe accomplished with utilization of a relatively small amount ofresources (e.g. relatively small amount of circuits, memory, etc.). Itis appreciated that the present invention can be implemented tofacilitate generation of modulated signals that are compatible with avariety of different modulation schemes. In one embodiment, presentinvention modulation is utilized in frequency synthesis. It is alsoappreciated that the present invention can be compatible withfacilitating realization of a number of objectives, including EMIreduction, encryption, radio communication etcetera.

General Modulated Frequency Synthesizing

FIG. 1A is a block diagram of exemplary modulation frequency synthesizer10 in accordance with one embodiment of the present invention. In oneembodiment, frequency synthesizer 10 is a modulation frequencysynthesizer. Frequency synthesizer 10 includes phase lock loopcontroller 20 and phase lock loop component 30. Phase lock loopcontroller 20 is communicatively coupled to phase lock loop component30. In one embodiment of the present invention, phase lock loopcontroller 20 includes modulation control pattern generation component21.

The components of frequency synthesizer 10 cooperatively operate toperform frequency synthesis. Phase lock loop component 30 creates amodulated output signal. In one embodiment, phase lock loop component 30creates a frequency modulated output signal. In one exemplaryimplementation, the frequency modulation is a spread spectrummodulation. Phase lock loop controller 20 controls phase lock loopcomponent 30 in the generation of the output signal. Modulation controlpattern generation component 21 generates a modulation controlindication utilized by phase lock loop controller 20 to control thephase lock loop component 30.

It is appreciated that the modulation control indication can correspondto a variety of patterns, including cyclical, non-cyclical, standard,non-standard, linear, non-linear, etcetera. In one embodiment a standardpattern or curve is generate by mathematical calculation, which usuallybut not necessarily has a nice and simple repeatable shape. In oneexemplary embodiment, the modulation control indication corresponds to aspread spectrum modulation. In one exemplary implementation, themodulation control indication corresponds to a fractional modulation.

FIG. 1B is a block diagram of components of modulation phase-locked loop(PLL) frequency synthesizer 200, in accordance with one embodiment ofthe present invention. Modulation phase-locked loop (PLL) frequencysynthesizer 200 is similar to modulation frequency synthesizer 10. Forexample phase lock loop component 220 is similar to one embodiment ofphase lock loop component 30 and phase lock loop controller 230 issimilar to one embodiment of phase lock loop controller 20. Modulationphase-locked loop (PLL) frequency synthesizer 200 includes referencefrequency source 210, phase lock loop component 220, phase lock loopcontroller 230 and driver 240. Frequency source 210 is communicativelycoupled to phase lock loop component 220 which is communicativelycoupled to phase lock loop controller 230 and driver 240. In oneembodiment, modulation phase-locked loop frequency synthesizer 200 is aspread spectrum modulation phase-locked loop frequency synthesizer.

In one embodiment, phase lock loop component 220 includes a phasefrequency detector 221, an adjustment component 222, a voltagecontrolled oscillator 223, and a feedback loop divider 224. Thecomponents of phase lock loop component 220 are communicatively coupledsequentially to form a phase lock loop. Phase frequency detector 221 iscoupled to adjustment component 222 which is coupled to voltagecontrolled oscillator 223. Voltage controlled oscillator 223 is coupledto feedback loop divider 224 which in turn is coupled back to phasefrequency detector 221. In one embodiment, frequency synthesizer 200facilitates the generation of multiple signal frequencies from areference frequency F_(R).

The reference frequency F_(R) is provided by reference source 210. Inone embodiment, multiple reference signal frequencies can be derivedfrom a common source or time base. The time base may be forwarded from acrystal oscillator 211. As such, the output from the oscillator 211 isreferred to as the initial base reference frequency F_(XO). The initialbase reference frequency F_(XO) can be divided down. For example, aninteger divider 212 can be coupled to the output of the oscillator 211and utilized to divide the initial base reference frequency F_(XO). Theinteger divider 212 produces a reference frequency F_(R) which isforwarded to phase lock loop component 220.

The reference frequency F_(R) can be tuned using, for example, a spreadspectrum phase-locked loop (PLL) as part of a frequency synthesizer.Phase lock loop component 220 makes frequency modulation adjustmentsbased upon control instructions from phase lock loop controller 230. Inone embodiment, phase lock loop component 220 makes frequencyadjustments directed to modulating the signal in accordance with desiredpatterns. For example, the desired patterns can be standard or nonstandard, linear or non linear, etc.

In one embodiment, phase frequency detector (PFD) 221 compares thereference frequency F_(R) received from reference frequency source 210with the feedback frequency F_(FB). Phase frequency detector 221generates a phase error or “error” signal based on the phase orfrequency differences between the reference frequency F_(R) and thefeedback frequency F_(FB). The phase and/or frequency error indicationfrom the phase frequency detector 221 can be adjusted by adjustmentcomponent 222. In one embodiment, adjustment component 222 filters thesignal. In one exemplary implementation, the phase and/or frequencyerror signal is forwarded to a filter included in adjustment component222, such as a low pass filter for example. In addition to the filter, acharge pump can be included in adjustment component 222 and used tocharge a voltage based on, for example, the feedback frequency leadingor lagging the reference frequency F_(R). The output of adjustmentcomponent is forwarded to voltage controlled oscillator 223.

The voltage controlled oscillator VCO 223 generates an output signal forthe frequency synthesizer 200. Depending on the drive requirements, adriver 240 can be utilized to adjust the output signal power.

As shown, the feedback frequency F_(FB) is a frequency from thevoltage-controlled oscillator (VCO) 223 modulated by feedback loopdivider 224 under the control of phase lock loop controller 230. Whileoscillator 223 produces an output signal F_(VCO) proportional to avoltage applied thereon, the feedback loop divider 224 divides F_(VCO)in accordance with modulation controls from phase lock loop controller230. The frequency of the F_(VCO) output signal from the synthesizer 200can be tuned and/or modulated by changing the feedback loop divide value(also referred to as “P”) within the feedback loop divider 224. Thedivide value acts as a denominator in dividing the frequency of theoutput signal F_(VCO). In one embodiment of the present invention,feedback divider 224 is a counter and the divide value is the modulo orMOD value. It is appreciated that a variety of divider techniques,including dual modulus or multi-modulus dividers, can be utilized toimplement feedback loop divider 224. The divide value is provided bymodulation control pattern generation component 231.

It is appreciated that the present invention systems and methods areflexible and can be implemented in a variety of configurations. It isalso appreciated an exemplary present invention phase lock loopcontroller can be compatible with realization of a variety of phase lockloop control schemes. In one embodiment, the modulation controlindication includes an indication of a PLL control state and or controlpattern. The PLL can be controlled by many signals, such as feedbackdivide value P, charge pump current I_(P), VCO gain K_(VCO), feedbackclock delay t_(d), etc. A set of one or a plurality of these signals orcomponents used in modulating PLL is defined as a PLL control state. Asequence of PLL control states is also called control pattern. A set ofone or a plurality of PLL operation signals, such as VCO frequencyf_(VCO) and voltages on several nodes of the loop filter, is defined asPLL operation state.

In one embodiment, the modulation control pattern generator 21 receivesmodulation information (e.g., including information derived from adesired PLL operation state sequence) as input and generates amodulation control pattern as output to control the PLL operation at adesired sequence of operation states. It is appreciated that the controlpattern can include a variety of PLL control state components. In oneembodiment, the control pattern is a sequence of P values. In oneembodiment, the control pattern is a sequence of P values and chargepump current I_(P)'s. In one embodiment, the PLL operation statesequence comprises VCO frequency f_(VCO) sequence (e.g., a frequencyprofile). In one embodiment, the PLL operation state comprises twovoltage signals on two loop filter nodes.

The modulation control pattern generator can include a modulationfeedback loop. The modulation feedback loop accepts modulationinformation as input and provides PLL control pattern information as anoutput. The modulation feedback loop can include auxiliary logiccircuits that manipulate the input and output. In one embodiment, theinput includes a standard Hershey Kiss pattern and modulation errorcompensation vectors. In one embodiment, the spread configurationinformation is first manipulated by a logic circuit to simplify an inputinterface. In one exemplary implementation, the output control patternis first manipulated by a logic circuit to fit requirements of a PLLfeedback counter interface.

FIG. 1C is an exemplary architecture diagram of an exemplary modulationcontrol pattern generator feedback loop 150 in accordance with oneembodiment of the present invention. In one exemplary implementation,the feedback loop 150 controls at least one quantity called themodulation control quantity. The modulation control quantity ismanipulated in the loop and the value of the modulation control quantitychanges in accordance with the manipulation. In one embodiment, themanipulation includes modulation and compensation as a modulationcontrol quantity propagates around the feedback loop. In one exemplaryimplementation, modulation is performed in accordance with a PLLoperation state contribution and further compensated with a PLL controlstate contribution. In one embodiment, a controlled quantity is fornegative feedback. The feedback loop 150 accepts modulation influencethat changes the value of a control quantity. The feedback loop 150 canalso further compensate the changed quantities to achieve a negativefeedback loop control goal.

In FIG. 1C, mixer 158 accepts PLL operations state contributions tomodulate modulation control quantities. The current modulation controlquantities 156 are modulated with PLL operation state contributionsignal 159 into modulated control quantity value 157 by mixer 158. ThePLL operation state contribution signal 159 signal can also be calledthe modulation signal or modulation influence. A modulated controlquantity 157 is compensated by a PLL control state contribution 151 incompensator 152 which outputs a PLL control state 153 and futuremodulation control quantities 154. In one exemplary implementation, foreach PLL control state, there is an associated contribution.Compensation component 152 compensates modulation control quantitieswith PLL control state contributions and selects the associated PLLcontrol state as a modulation pattern. The best contribution can bechosen by an algorithm implemented in the compensation circuit. Then amodulation control quantity can be compensated with the best PLL controlstate contribution. In one exemplary implementation, the compensatedmodulation control quantities are then generated by summing up themodulated control quantities and the selected best contribution. Thecompensated or future modulation control quantities 154 return to thestarting point, for example, a storage element 155 in digital circuit,to close the loop. The quantities that come back to the starting pointare referred to as “future” modulation control quantities 154, sincethey enter the next cycle of the loop in the future. The PLL controlstate output 153 associated with the modulated and compensatedmodulation control quantity is forwarded to the PLL control circuit.

It is appreciated a variety of algorithms can be utilized to implementthe contribution selection in the compensation circuit 152 thatcorresponds to a modulation goal or objective. In one embodiment, theobjective is to minimize the deviation from initial state of thequantities. In another embodiment, the goal is to compensate for minimumweighted error sum of compensated quantities. In another embodiment, thegoal is to minimize the deviation from target quantities which can beeither constants or variables. Yet in another embodiment, the goal is tominimize the quantity deviation from zero.

In one embodiment with multiple control quantities, the control loop canhave alternative architecture. In one embodiment, several loops can beused to work together.

In one embodiment with multiple control quantities, the control loop canhave alternative architecture. In one embodiment, several loops can beused to work together.

While it is appreciated that the control pattern can include a varietyof PLL control state components, the following descriptions focus on thePLL feedback loop divide value so as not to unnecessarily obfuscateembodiments of the present invention. A PLL feedback loop usuallyincludes a divider (e.g., 224) to divide down a VCO frequency (e.g.,F_(VCO)). The divider is often referred to as a PLL feedback divider orfeedback counter. It can also be referred to as a P counter, P divider,M divider, M counter, N divider and/or N counter. In one embodiment ofmodulation phase-locked loop (PLL) frequency synthesizer 200 shown inFIG. 1B, phase lock loop controller 230 forwards PLL feedback loopdivide values to divider 224.

Again, it is appreciated that the present invention systems and methodsare flexible and can be implemented in a variety of configurations. Itis also appreciated an exemplary present invention phase lock loopcontroller can be compatible with realization of a variety of phase lockloop control schemes. FIG. 2 is a block diagram of exemplary phase lockloop controller 290 in accordance with one embodiment of the presentinvention. Phase lock loop controller 290 generates a sequence of valuesand forwards the values to a PLL to modulate a synthesized frequency. Inone embodiment, the sequence of values are feedback divider values Pwhich can be accepted by a straight forward integer divider. In anotherembodiment, the values include a base P and offset P values which can beaccepted by an offset divider. In one embodiment, the phase lock loopcontroller 290 includes a modulation pattern generator 293 and a dividercontroller 292. The modulator generates the offset P values. The dividercontroller accepts the offset P values (PO) and base P values (Pbase),then generate total P values (P) and forwards to P divider.

The PLL feedback divider value, or P value, can be fixed or variableduring frequency synthesis. When P is fixed, it is called directsynthesis. Since P counter is an integer counter, direct synthesis canmultiply the reference frequency by an integer, which is P here. In oneembodiment, to multiply the reference frequency by a fractional number,P values are changed in a sequence or pattern so that the average Pvalue is expressed as Pave=N+n/d, where N, n and d are integers. This iscalled fractional-N synthesis. In one exemplary implementation, thecircuit to change P values is called a fractional-N modulator. Thestraight forward P divider together with the fractional-N modulator isalso called a fractional-N divider. In fractional-N synthesis, the VCOoutput frequency is ideally a horizontal line in time domain.

It is appreciated that embodiments of the present invention arecompatible with a variety of frequency synthesis configurations. In oneexemplary implementation, spread spectrum synthesis is performed. Inspread spectrum synthesis, the VCO output frequency forms a specialshape output (e.g., triangle shape, Hershey kiss candy shape, etc.). Inone embodiment, a special shape output is utilized so that the powerspectrum amplitude of VCO output is reduced. In one exemplaryimplementation, a special P sequence is utilized. In one embodiment, thecircuit to generate the special P sequence is called a spread spectrummodulator.

Phase lock loop controller 290 can be configured to implement controlindications compatible with a spread spectrum control scheme and/or afractional control scheme. In one embodiment, the modulator is capableof generating spread spectrum control pattern. In another embodiment,the modulator is capable of generating fractional-N control pattern. Itcan be a 0% spread special case of a spread spectrum modulator, or oneof the fractional-N modulators described in commonly owned “U.S. patentapplication Ser. No. 10/947,519 by Shuliang Li, filed on Sep. 22, 2004,entitled “FREQUENCY SYNTHESIZER HAVING A MORE VERSATILE AND EFFICIENTFRACTIONAL-N CONTROL CIRCUIT AND METHOD” and “FREQUENCY MODULATOR,CIRCUIT, AND METHOD THAT USES MULTIPLE VECTOR ACCUMULATION TO ACHIEVEFRACTIONAL-N FREQUENCY SYNTHESIS”, application Ser. No. 11/172,691,which are incorporated herein by this reference.

Many of the following descriptions are described relative to time. Inone embodiment, a spread spectrum modulator is driven by a clock. In oneexemplary implementation, the clock is the PLL feedback divider output.At each active clock edge, the modulator advances one step, going from acurrent status or value to a new status or value. In one embodiment, thestatus includes values of registers and buses. In one exemplaryimplementation, the values correspond to modulation control quantityvalues. In one exemplary implementation, the status in the modulator iscalled “current” status before advancing a step. The expected statusafter the advance is called “future” status. They can also be referredto as status of “current” and “future” steps, time steps or time. In oneembodiment, a spread spectrum modulator includes a feedback loop whichcontrols at least one control value. In one embodiment, the primarycontrol value is “modulation error”, or simply “error”. This “modulationerror” value mimics the phase error of a PLL, but can have a differentscale and/or reference point. In one exemplary implementation, at leastone future error is generated based on current and/or early status ateach modulation step. The best or optimized future error replaces thecurrent error when the step advances.

The spread spectrum modulator generates at least one output value thatdirectly or indirectly controls the PLL. As the modulator advances intime step, the output value(s) form a pattern or sequence. It isreferred to as spread spectrum control pattern or sequence. In oneembodiment, the value is feedback divider offset value PO. In anotherembodiment, it is feedback divider value P.

It is appreciated that embodiments of the present invention can beimplemented on a single silicon chip. It is also appreciated that thepresent invention can be implemented in hardware, firmware, and/orsoftware.

Spread spectrum clock synthesis can be utilized for a variety ofapplications. For example, spread spectrum clock synthesis offers anefficient solution to system electromagnetic interference (EMI)reduction. In one embodiment, a Hershey kiss shape frequency profileprovides good EMI reduction since it yields flat-topped power spectrumcurve in ideal condition. This means power is more evenly distributed indesired frequency band. Hence it reduces the peak value of powerspectrum. In another embodiment, a triangle shape frequency profileyields a power spectrum curve with two sides high, meaning more power isdistributed on the two sides. This causes its maximum value of the powerspectrum to be higher than a flat-topped one yielded by Hershey Kissshape spread of the same spread amount. Although the EMI reduction for atriangle spread may be less than Hershey Kiss spread, the trianglespread has advantages. A triangle spread is easy to implement and itsfrequency slew rate (absolute value) is constant. For the same spreadpercentage of a frequency, the triangle shape has significant smallermaximum frequency slew rate. The triangle shape allows the down streamsystem to track the frequency curve better and has more timing budget.In one embodiment, a Hershey kiss profile has variable slew rate andreaches maximum absolute value at its peaks, which is hard for some downstream system to handle. A triangle spread spectrum frequency curve is alinear curve. A Hershey Kiss curve is non-linear curve. For frequencycurves like triangle or Hershey Kiss shape, they are also calledstandard curve in this patent.

For both triangle and Hershey Kiss shape frequency spread, the PLLfeedback divider is modulated with a finite length pattern periodically.In conventional techniques, a look-up table that is implemented inmemory on chip is used to store feedback divider patterns. Programmablememory is preferred for storing the look-up table for changing spreadconfiguration conveniently. However, this kind of memory is large inarea and usually not like circuits that are easily shrinkable withtechnology improvement. The memory circuit size do not usually shrinkmuch in new process, because the storage elements of programmable memoryare special. Thus, when normal circuits shrink, the area percentage ofprogrammable memory on a clock chip increases. When traditional systemsattempt to use multiple spread configurations, the programmable memoryused to store the look-up tables become increasingly expensive toimplement both in terms of economic cost and in physical space.

Meanwhile, the P value associated with the best vector is forwarded tothe P counter controller. As the clock drives this modulation feedbackloop 3000 to run cycle by cycle, a sequence of P values (PLL controlpattern) is generated. The phase lock loop (PLL) P counter (e.g.,divider 224) loads these P values one by one each time a full countingis finished. Thus, the desired VCO frequency curve is generated bymodulating the P counter or divider. It is appreciated there are avariety of ways to implement modulation feedback loop architecture 3000.

FIG. 3B is a block diagram of exemplary frequency control patterngeneration system 300 in accordance with one embodiment of the presentinvention. In one embodiment, frequency control pattern generationsystem 300 can be utilized similar to frequency control patterngeneration component 231 and/or modulation control pattern generationcomponent 21. In one embodiment, frequency control pattern generationsystem 300 includes a modulation loop for introducing modulationinfluence on a modulation error. In one exemplary implementation, amodulation signal is input to a modulation loop. The modulation loop canalso include error correction vector accumulation. In one embodiment,each potential feedback loop divide value P is associated with an errorcorrection vector and produces associated future error.

Frequency spreading control pattern generation system 300 includes inputmodulation signal mixer 310, future error generation component 320,error selection component 330, pattern value selection component 340 andselected error register 350. Input modulation signal mixer 310 iscommunicatively coupled to future error generation component 320 whichin turn is communicatively coupled to error selection component 330.Error selection component 330 is communicatively coupled to patternvalue selection component 340 and selected error register 350.

The components of frequency spreading control pattern generation system300 co-operatively operate to provide feedback loop divider information.Input modulation signal mixer 310 produces a modulated error signal.Future error generation component 320 produces a plurality of errorsignals based upon the modulated error signal and error adjustmentvectors. Error selection component 330 selects one of the plurality oferror signals. Pattern value selection component 340 selects a patternvalue based upon the error selected by error selection component 330.Selected error register 350 stores the selected one of the plurality oferror signals.

In one embodiment, input modulation signal mixer 310 mixes an inputmodulation signal or value with the “currently” selected error signal orvalue. In one exemplary implementation, the input modulation signal isnon linear. For example, the input modulation signal can have curves andpeaks (e.g., a curve similar to a Hershey kiss candy). In anotherexemplary implementation, the modulation signal is linear (e.g.,triangular). It is appreciated that the input modulation signal can havea variety of different configurations, including standard and/ornon-standard schemes (e.g., patterns, curves, etc.).

Future error generation component 320 generates potential future errors.In one embodiment, future error generation component 320 receives aplurality of error correction vectors. Error combination component 320combines the modulated error signal with the error correction vectors.In one embodiment, the vectors are organized in a monotonic order andthe output of potential future errors are organized in a correspondingmonotonic order. In one exemplary implementation, each vector andpotential future error are assigned corresponding indexes based uponrelative position in the monotonic order.

Error selection component 330 selects an error and forwards the selectederror to selected error register 350. In one embodiment, error selectioncomponent 330 includes a delta-sigma selection component. It isappreciated that the present invention is readily implemented with avariety of error selection schemes or techniques. In one exemplaryimplementation, a “best” error is selected. Further explanation of errorselection in accordance with one embodiment of the present invention isdescribed in other sections below. Error selection component 330 alsoforwards identification of the selected error signal to pattern valueselection component 340.

In one embodiment, pattern value selection component 340 receives aplurality of predetermined pattern values and selects one of thepredetermined pattern values based upon the information received fromerror selection component 330. In one embodiment, the selected patternvalue contributes to the control value forwarded to feedback loopdivider (e.g., feedback loop divider 224). The pattern values can berandom or non-random. In one exemplary implementation, the patternvalues received by pattern value selection component 340 are organizedin a monotonic order corresponding to monotonic order of the pluralityof error correction vectors and potential future errors. Pattern valueselection component 340 utilizes an index indication of the selectederror value from error selection component 330 to select the patternvalue. In one embodiment of the present invention, the pattern valueselection component 340 includes a multiplexer. In one exemplaryimplementation, the selected error identification and/or index valueforwarded from error selection component 330 is utilized as theselection inputs to the multiplexer.

Turning now to FIG. 3C, an example is shown in which three errorcorrection vectors are shown. That is, as shown in FIG. 3A, there are nvectors that are provided as inputs into the error combination component320. In example of FIG. 3B, n=3, in which here error vectors V₁, V₂, andV₃ are chosen as an example of how the iterative selection process takesplace. Specifically, two negative error vectors at P and P+1 are shownas V₁ and V₂. One positive vector P+2 is shown as V₃.

In the example of FIG. 3B, a resolution of 256 is chosen between Pvalues (e.g., between P and P+1, and between P+1 and P+2). Each vector,V, is shown extending from the average P value P_(AVERAGE) to theinteger P values of P, P=1, and P+2. The amount of error vector V₁ in anegative direction is cumulative of P_(AVERAGE) to P+1, and P+1 to P.The amount between P_(AVERAGE) and P+1 is −32, in FIG. 6. The amountbetween P+1 and P is −256, making the cumulative amount of error vectorV₁ equal to −288. The amount of error vector V₂ is shown as −32, and theamount of V₃ is 256−32, or +224. It is understood that there can be morethan three error vectors and the numbers provided for each vector valuesare merely examples.

It is appreciated that modulation patterns are scalable. Differentmodulation frequencies and spread amounts can be generated by scalingone modulation curve. In one exemplary implementation, a single standardmodulation curve values can be stored in a relatively small memory andmultiple curves are generated (e.g., by circuits or logic). By scalingcycles in the X direction (e.g., a direction corresponding to time) themodulation frequency can be changed. By scaling in the Y direction (e.g.a direction corresponding to amplitude) the spread amount can bealtered. In one embodiment, the amplitude and length of a modulationsignal cycle can be altered. In one exemplary implementation, themodulation signal pattern amplitude is determined based upon theresolution, spread percentage and the average divide value. For example,the amplitude equals the resolution times spread % times average dividevalue. In another embodiment, resolution is scalable, and the frequencyspread percentage is reverse proportional to resolution.

It is also appreciated that auxiliary circuit can be used to simplify orreduce input interface. For example, if the resolution and one vector V₁are known, other vectors can be determined by math. That is, V₂=V₁+resolution, and V₃=V₁+2*resolution=V₂+resolution. So an auxiliary logiccan be used to accept resolution and a vector to produce all vectors. Inone embodiment, when changing the average P, only the vectors need to bechanged and the resolution and one vector are enough to ascertain othervectors. In one embodiment, a modulation curve is scalable and vectorscan be derived, thus only scaling factors (e.g., defining modulationfrequency and spread amount), resolution and one vector (definingaverage P value and selectable P values) are needed to configure themodulation loop.

FIG. 4 is a flow chart of exemplary frequency control pattern generationmethod 400 in accordance with one embodiment of the present invention.Frequency spreading control pattern generation method 400 controlsmodulation “error” in a modulation feedback loop and generatesindication of PLL frequency adjustment. In one embodiment, the frequencyadjustment indications are directed to facilitating realization of aspread spectrum output.

At block 410, a modulation signal is received. It is appreciated thatthe modulation signal can have a variety of configurations. Themodulation signal can be linear or non-linear. The modulation signal canalso have a standard or non-standard configuration. It is alsoappreciated that the modulation can be directed towards a number ofobjectives, including EMI reduction, signal encryption, radiocommunication, etcetera.

In block 420, the modulation signal is mixed with a present or currenterror signal to produce an modulated error signal. In one embodiment,the initial error signal is a present error signal or value and themodulation signal modulates or alters the present error signal. In oneexemplary implementation, mixing the initial error signal with themodulation signal results in the base of the error signal “following” ortracking a modulation pattern. It is appreciated the modulation signalcan be scaled in accordance with embodiments of the present invention.

The modulated error signal is merged with a plurality of errorcorrection vectors to produce a plurality of potential “future” errorsignals at block 430. In one embodiment, the vector is based upon anaverage divide value and an offset from the average divide value withcertain resolution.

At block 440, one of the potential “future” error signals is chosen. Inone exemplary implementation, the chosen future error signal correspondsto a minimal error. In one embodiment, the minimal error is the errorthat is closest to a target error or a zero-cross point in a monotonicorder.

At block 450, a feedback loop divide value is picked based upon thechosen “intermediate” error signal. In one embodiment, the chosen“future” error signal becomes a current error and is utilized insubsequent iterations of block 410 error signal and modulation signalmixing.

In one embodiment, a “best” error is one that keeps the final outputsignal close or tight to the modulation pattern around a targetfrequency. In some exemplary implementations, the selection of “best”error is directed towards an error value that provides a tightcorrelation with the modulation pattern. In one embodiment, a frequencysynthesizer (e.g., frequency synthesizer 10) includes a zero cross errorselection spectrum spreading control pattern generation component forgenerating a spread spectrum control pattern utilized by the phase lockloop controller to control the phase lock loop component. In oneembodiment of the present invention the resources (e.g., circuits)utilized to implement best error selection are relatively small andfast. It is appreciated that present invention “best” error selectiontechniques can be utilized with a variety of different modulationschemes, including fractional-N and spread spectrum modulation schemes.

Zero Crossing Best Error Selection

FIG. 5A is a block diagram of exemplary cross zero best error selectionsystem 500 in accordance with one embodiment of the present invention.In one embodiment, cross zero best error selection system 500 isutilized in error selection component 330 of system 300 shown in FIG.3A. Cross zero best error selection system 500 includes error inputinterface 510, most significant bit (e.g., sign bit) summation component520 and feed back multiplexer 530. Error input interface 510 iscommunicatively coupled to most significant bit summation component 520which is communicatively coupled to feed back multiplexer 530.

The components of cross zero best error selection system 500cooperatively operate to select a best error. Error input interface 510receives a plurality of future error values. The target error value iszero or is manipulated to be so. The errors are arranged in a monotonicorder for the multiplexer selection index. Most significant bitsummation component 520 sums most significant bits of the future errorvalues. In one embodiment, the most significant bit summation componentis an adder that adds the sign bit. In one embodiment the sign bit isthe most significant bit. In one exemplary implementation, the error isexpressed in two's complimentary binary number and a negative number isindicated by a most significant bit with a logical one value. Theposition or index where the error crosses zero is indicated where themost significant bit changes from a logical one to a logical zero whichcorresponds to a sign change in the error. In one embodiment, thesummation of the most significant bits corresponds to an identificationof the selected error value. In one exemplary implementation, thesummation of the most significant bits is an index value associated withthe selected error value. Feedback multiplexer 530 feeds back a selectederror value based upon the summation of the most significant bits.

It is appreciated that present invention cross zero selection systemscan be incorporated in a variety of modulation control patterngeneration systems. FIG. 5B is a block diagram of an exemplaryimplementation of frequency spreading control pattern generation system300 utilizing a cross zero best error selection system. In the presentexample, error selection component 330 is implemented with error inputinterface 131, most significant bit summation component 332 and feedback multiplexer 333 which are similar to error input interface 510,most significant bit summation component 520 and feed back multiplexer530 of FIG. 5A. The sum of the most significant bits from mostsignificant bit summation component 332 is forwarded to control valueselection component 340 and to MUX 333 which forwards the selected errorto selected error register 350.

Cross zero best error selection methods of the present invention can beutilized to select a “best” error indication. In one embodiment, anerror corresponding to the point or close to the point where the “error”crosses zero is selected as the “best” error. In one embodiment, apresent invention a cross zero best error selection method isimplemented in software. In one exemplary implementation of multiplevector modulation, best error selection in accordance with the presentinvention achieves results similar to sophisticated logic, such as:i _(best) =i such that (e _(i-1)<0 and e _(i)>=0)with relatively simple logic. A present invention cross zero selectioncan be implemented in hardware, firmware and/or software. FIG. 6 is aflow chart of exemplary cross zero best error selection method 600 inaccordance with one embodiment of the present invention.

In one embodiment similar to FIG. 5A, n errors are received. The rangeof the most significant bit summation is 0 to n. There are n+1 numbersfor the sum. The multiplexer is designed to be able to handle thispotential n+1 selections. If errors e₀, e₁, . . . , e_(n) are sorted inascending order, there are several methods to handle index selection. Inone exemplary implementation the selected index comes from the mostsignificant bit summation. In one embodiment, the summation n+1 isaltered to n by logic. In another embodiment, the multiplexer uses index0 to n to select inputs normally and uses n+1 to select the same inputas index n. In another embodiment, the most significant bit summation ofthe errors excludes the largest error e_(n) so that the index range isfrom 0 to n−1.

At block 610, a plurality of error values are received. In oneembodiment the error values are “future” errors. In one embodiment,future contribution vectors are sorted in monotonic order and the future“errors” generated by them are also in a corresponding monotonic orderand at some index the “error” crosses zero. For example, the pluralityof received error can be a combination of a “current” error modulatedwith a modulation signal and adjusted by correction vectors. In oneexemplary implementation, the plurality of error values are receivedfrom a future error generation component.

The most significant bits of the error values are summed at block 620.In one exemplary implementation, the result of summing the mostsignificant bits is equal to an index of a cross zero point.

In block 630, one of the error values is selected based upon results ofthe summing. In one embodiment, the selected error is the error closestto the cross zero point. The selecting can include multiplexing theerrors in accordance with the results of most significant bit summing ofthe error values.

In block 640, the results of the summing are forwarded as anidentification of the selected one of the error values. In oneembodiment, the identification of the selected error value is an indexcorresponding to the “position” of the selected value in a monotonicorder. In one embodiment the result of the selecting is forwarded as anerror feedback value.

In one embodiment of the zero-crossing best error selection method theerrors are sorted in the monotonic order wherein the cross zero point isan index corresponding to a point in the monotonic order of errors.

Enhanced Noise Shaping in a Spread Spectrum Modulator

FIG. 7 is a block diagram of a spread spectrum modulator 700 that iscapable of enhanced noise shaping, in accordance with one embodiment ofthe present invention. The modulator 700 is an extension of thefrequency spreading control pattern generation system 300 of FIG. 3B, inone embodiment. As such, it is intended that similarly numbered blocksin FIGS. 3B and 7 perform similar functions. In other embodiments, thespread spectrum modulator 700 provides fractional-N synthesis withenhanced noise shaping features.

The modulator 700 includes a vector selector engine that iterativelyselects amongst a plurality of vectors V₁ through V_(n), dependent onwhich vector when summed with a modulated error produces the best errorclosest value nearest a target desired value.

The spread spectrum frequency modulator 700 includes an input modulationsignal mixer 310, error combination component 320, selected errorregister 350, accumulator 750, multiplexer 740, multiplexer 770, and anoise shaping module 760 that are all communicatively coupled.

The components of the spread spectrum modulator 700 co-operativelyoperate to provide feedback loop divider information to a divider of aPLL of a frequency synthesizer, in one embodiment. In the presentembodiment, the PLL comprises a divider. With spread spectrum modulator700, the PLL is capable of synthesizing fractional-N or spread frequencyin embodiments of the present invention.

In particular, the input modulation signal mixer 310 produces amodulated error signal from the current best error stored in register350, and an input modulation signal 305 that acts as a target signal.The input modulation signal 305 is non-linear, in one embodiment. Forexample, the input modulation signal can have curves and peaks in whichthe spread spectrum of the synthesized signal has reduced amplitude andincreased bandwidth. In another exemplary implementation, the inputmodulation signal 305 is linear (e.g., triangular).

The error combination component 320 produces a plurality of futureand/or compensated error signals based upon the modulated error signal311 from the input modulation signal mixer 310, as previously describedin FIG. 3B.

In addition, in one embodiment, as shown in FIG. 7 the modulator 700includes an accumulator 750 for selecting the index i_(best). The indexi_(best) is associated with the best error, future e_(best), of the nextmodulation step. That is, the index, i_(best), provides anidentification of the future best error, future e_(best), of the nextmodulation cycle.

In one embodiment, the accumulator 750 implements a cross zero methodfor selecting the index, i_(best), as previously described in relationto FIGS. 5A and 5B, in accordance with one embodiment of the presentinvention. The accumulator 750 sums the most significant bits of theerrors as outputted by the error combination component 320. As the valueof the accumulator 750 crosses zero, the index, i_(best), thatcorresponds to the best error, future e_(best), of the next modulationcycle can be determined. In other embodiments, the index, i_(best), isselected using other types of selectors, such as the error selectioncomponent 330 of FIG. 3.

Additionally, the spread spectrum modulator 700 includes a noise shapingmodulator circuit 760 that is coupled to the PLL of a frequencysynthesizer for increasing a rate of sign change of a plurality oferrors used to select a divider count value. The divider count value isbased upon an accumulated error of the plurality of errors, as will bedescribed more fully below.

In particular, the noise shaping modulator 760 takes as inputs theindex, i_(best), from the accumulator 750 and the best error of thecurrent modulation cycle, current e_(best). More specifically, whenclocked, the current best error, current e_(best), is obtained from themultiplexer 740 and stored in the register 350. Thereafter, the currentbest error, current e_(best), is accessed from the register 350 by thenoise shaping modulator 760.

In addition, during the same clock cycle, the current best error,current e_(best), is modulated by the input modulation signal at themixer 310 to produce the modulated error signal 311. Also, the errorcombination component 320 produces a plurality of error signals, whichis delivered to the accumulator 750 to determine index, i_(best), aspreviously described. The index, i_(best), is then delivered to thenoise shaping modulator 760 in the same clock cycle.

Thereafter, the noise shaping modulator 760 modulates the index,i_(best), based on the accumulated error of the plurality of errors, aswill be described below in relation to FIGS. 8A and 8B. In particular,the noise adjusted i_(best) is denoted by noise adjusted index, j.

The noise adjusted index, j, is used for selecting feedback loop dividercount values used for dividing a frequency of the output signal from thefrequency synthesizer. In particular, the phase count selectioncomponent 770 selects a feedback loop divider count value, P, based uponthe noise adjusted index, j. This feedback loop divider count value, P,is then fed to a divider (e.g., divider 224 of FIG. 1B) of a PLL in thefrequency synthesizer.

The spread spectrum modulator 700 also includes a multiplexer 740 thatselects the noise adjusted best error, noise adjusted e_(best), alsoknown as the future error, of the next modulation cycle according to thenoise adjusted index, j. This best error, noise adjusted e_(best), ofthe next modulation cycle is held until the next clock cycle. With thenext clock cycle (e.g., leading or falling edge), the best error of thenext modulation cycle, noise adjusted e_(best), is stored in theregister 350 to become the current error, current e_(best), of the nextmodulation cycle.

FIG. 8A is a block diagram of the noise shaping modulator 760 of FIG. 7,in accordance with one embodiment of the present invention. The noiseshaping modulator 760 is capable of shaping the noise of the signaloutput of an associated frequency synthesizer by shifting the noise to ahigher frequency and providing an increased rate of sign change of thenoise around a target signal, in embodiments of the present invention.As such, the spread spectrum modulator 700 of FIG. 7 has betterfrequency profile and improved EMI performance.

As described previously, the noise shaping modulator 760 takes asinputs, the index, i_(best), from the accumulator 750, and the currentbest error, current e_(best) from the register 350. The noise shapingmodulator 760 is able to increase the rate of sign change of theplurality of errors.

The noise shaping modulator 760 includes an accumulator 810 for summinga plurality of errors from the modulator circuit 700 of FIG. 7. As such,the accumulator 810 generates an error sum value (esum_(m)). Inparticular, the accumulator 810 sums the current error, currente_(best), and a previously summed error, esum_(m-1), from the previousmodulation step.

As described previously, the current error, current e_(best), isselected from one of a plurality of error values compensated by positiveand negative vector values from an average value, P_(AVERAGE), equal toa fraction by which a divider in a phased lock loop divides a frequencyof an output signal of a frequency synthesizer, in one embodiment.

In addition, a delay module 820 is shown in the noise shaping modulator760. The delay module 820 stores the previously summed error,esum_(m-1), from the previous modulation step. In addition, the delaymodule 820 provides the previously summed error, esum_(m-1), to theaccumulator 810 in the next modulation step.

As shown in FIG. 8A, the noise shaping modulator 760 also includes anerror signal modulator 840 that is coupled to the accumulator 810. Theerror signal modulator 840 modulates the index, i_(best), based on theerror sum value to determine the noise adjusted index, j. The noiseadjusted index, j, is used for selecting feedback loop divider countvalues used for dividing a frequency of the output signal from afrequency synthesizer, as previously described.

In particular, the error signal modulator 840 modulates the index,i_(best), based on the most significant bit (MSB) output of the errorsum value, esum_(m). Specifically, the MSB indicates the sign of thesummed error, esum_(m), from the accumulator 810.

In one embodiment, the error signal modulator 840 increases the index,i_(best), by one when the MSB indicates the sign of the summed error,esum_(m), is negative (e.g., MSB=1). As such, the noise adjusted index,j, is determined as follows: j=i_(best)+1. The noise adjusted index, j,is used to select the P value as the feedback loop divider count valuein the PLL of the frequency synthesizer.

In another embodiment, the error signal modulator 840 decreases theindex, i_(best), by one when the MSB indicates the sign of the summederror, esum_(m), is positive (e.g., MSB=0). As such, the noise adjustedindex, j, is determined as follows: j=i_(best)−1. The noise adjustedindex, j, is used to select the P value as the feedback loop dividercount value in the PLL of the frequency synthesizer.

FIG. 8B is a block diagram of the noise shaping modulator 760 of FIG. 7,in accordance with one embodiment of the present invention. The noiseshaping modulator 760 is capable of shaping the noise of the signaloutput of an associated frequency synthesizer by shifting the noise to ahigher frequency and providing an increased rate of sign change of thenoise around a target signal, in embodiments of the present invention.As such, the spread spectrum modulator 700 of FIG. 7 has betterfrequency profile and improved EMI performance.

As described previously, the noise shaping modulator 760 takes asinputs, the index, i_(best), from the accumulator 750, and the currentbest error, current e_(best) from the register 350. The noise shapingmodulator 760 is able to increase the rate of sign change of theplurality of errors.

The noise shaping modulator 760 includes an accumulator 815 for summinga plurality of errors in the modulator circuit 700 of FIG. 7. As such,the accumulator 815 generates an error sum value (esum_(m)). Inparticular, the accumulator 815 sums the current error, currente_(best), and a previously summed error, esum_(m-1), from the previousmodulation step.

As described previously, the current error, current e_(best), isselected from one of a plurality of error values compensated by positiveand negative vector values from an average value, P_(AVERAGE), equal toa fraction by which a divider in a phased lock loop divides a frequencyof an output signal of a frequency synthesizer, in one embodiment.

In addition, a delay module 825 is shown in the noise shaping modulator760. The delay module 825 stores the previously summed error,esum_(m-1), from the previous modulation step. In addition, the delaymodule 825 provides the previously summed error, esum_(m-1), to theaccumulator 815.

As shown in FIG. 8B, the noise shaping modulator 760 also includes anerror signal modulator 845 that is coupled to the delay module 825. Theerror signal modulator 845 modulates the index, i_(best), based on theerror sum value to determine the noise adjusted index, j. The noiseadjusted index, j, is used for selecting feedback loop divider countvalues used for dividing a frequency of the output signal from afrequency synthesizer, as previously described.

In particular, the error signal modulator 845 modulates the index basedon the most significant bit (MSB) output of the previously summed errorvalue, esum_(m-1). Specifically, the MSB indicates the sign of thepreviously summed error value, esum_(m-1), as obtained from the delaymodule 825.

In one embodiment, the error signal modulator 845 increases the index,i_(best), by one when the MSB indicates the sign of the previouslysummed error value, esum_(m-1), is negative (e.g., MSB=1). As such, thenoise adjusted index, j, is determined as follows: j=i_(best)+1. Thenoise adjusted index, j, is used to select the P value as the feedbackloop divider count value in the PLL of the frequency synthesizer.

In another embodiment, the error signal modulator 845 decreases theindex, i_(best), by one when the MSB indicates the sign of thepreviously summed error value, esum_(m-1), is positive (e.g., MSB=0). Assuch, the noise adjusted index, j, is determined as follows:j=i_(best)−1. Again, the noise adjusted index, j, is used to select theP value as the feedback loop divider count value in the PLL of thefrequency synthesizer.

Although the embodiments of FIGS. 8A and 8B are described with the indexincreasing and decreasing by one according to the sign of the MSB, otherembodiments are capable of supporting increasing and decreasing theindex by one according to the opposing sign of the MSB. That is, whenthe MSB=0, the index, i_(best), is increased by one, and when the MSB=1,the index, i_(best), is decreased by one. Also, other embodiments arecapable of increasing or decreasing the index by a value other than one.Still other embodiments are capable of increasing or decreasing theindex by a variable number. That is, the index may be increased by afirst value, and decreased by a second value.

In still another embodiment, the range of the index is limited. That is,the range of the index is limited to a maximum value. As such, themodulated index cannot exceed the maximum value of the index on theupper range. For example, if i_(best)=i_(n), then the noise adjustedindex, j, is also equal to i_(n).

Also, the range of the index is limited to a minimum value. As such, themodulated index cannot exceed the minimum value of the index on thelower range. As such, the modulated index cannot go lower than theminimum value of the index on the lower range. For example, ifi_(best)=i₁, then the noise adjusted index, j, is also equal to i₁.

Still other embodiments are able to implement other techniques forlimiting the range of the index and modulated index.

FIG. 9 is a flow chart of exemplary frequency spreading control patterngeneration method 900 in accordance with one embodiment of the presentinvention. In particular, the method of FIG. 9 produces a signal ofselectable frequency with enhanced noise shaping, in accordance with oneembodiment of the present invention. The method of FIG. 9 can beimplemented within a spread spectrum modulator of a frequencysynthesizer. For instance, the method of FIG. 9 can be combined with themethod of FIGS. 4 and 6 to generate a frequency spreading controlpattern for use in a PLL, in one embodiment.

At 910, the present embodiment generates an error sum value by summing acurrent error in a current modulation step and a previous error (e.g.,previous error sum) from a previous modulation step. As such, the errorsum value is a sum of all the error values in previous modulation stepsand the current modulation step. Introduction of the error sum valueenables the present embodiments to achieve a higher frequency of achange of sign of the error from a target signal, thereby obtainingbetter frequency profile and improved EMI reduction.

In addition, the error sum value is quantized by determining a mostsignificant bit (MSB) of the error sum value. In particular, the indexis increased by one when the MSB indicates a sign of the error sum valueis negative, in one embodiment. Also, the index is decreased by one whenthe MSB indicates a sign of the error sum value is positive, in anotherembodiment.

At 920, the present embodiment modulates an index that is associatedwith a current error based on the error sum value. The current error ischosen from the best error associated with a vector of a P value thatgenerates the least error when compared with a target signal. Inparticular, the modulated index is used for selecting feedback loopdivider count values used for dividing a frequency of said signal. Thatis, the index that is modulated is fed to a feedback divider of a PLL.

In one embodiment, a range of the index is limited to a maximum value.In another embodiment, the range of the index is limited to a minimumvalue.

In another embodiment, current error is modified based on the error sumvalue. As such, the next error (e.g., next previous error) is generatedthat is associated with the next modulation step.

FIG. 10A is a diagram of the frequency response of a frequencysynthesizer without any noise enhancements of the present invention, inaccordance with one embodiment of the present invention. The diagram ofFIG. 10A illustrates that the modulated frequency of the output signal1010 from the frequency synthesizer does not follow the underlyingtarget signal 1009. In addition, the frequency jittering is not high,because the frequency of the change of sign of the error is not veryhigh.

FIG. 10B is a diagram of the frequency response of a frequencysynthesizer with noise enhancements of the present invention. Thediagram of FIG. 10B illustrates that the modulated frequency of theoutput signal 1020 from the frequency synthesizer follows the sameunderlying target signal as in FIG. 10A better than modulated frequencyof the output signal 1010 of FIG. 10A. Also, the frequency jittering ismuch higher, because the frequency of the change of the sign of theerror is much higher than that of FIG. 10A. As such, with the enhancednoise shaping of the present invention, the frequency synthesizer isable to achieve better EMI performance with better shape tracking. Thatis, the frequency synthesizer exhibits an improved reduction in EMI whencompared to frequency synthesizers that do not implement the enhancednoise shaping of the present invention.

First Order Accumulation for Generating a Standard Curve that is FurtherModulated to Generate a Desired Frequency Profile

FIG. 11A is a block diagram of a frequency synthesizer 1100A thatimplements first order accumulation to generate a linear standard curvethat is further modulated to generate a frequency profile, in accordancewith one embodiment of the present invention. The frequency synthesizeris capable of performing spread spectrum synthesis when generating aP-sequence of values used in a phase-locked loop of the frequencysynthesizer, in accordance with one embodiment of the present invention.

The frequency synthesizer 1100A comprises a system for modulating asignal to generate a standard curve. As shown in FIG. 11A, the frequencysynthesizer 1100A comprises a control circuit 1110, an accumulator 1120,a spread spectrum modulation loop 1130, and a phase-locked loop 1140,all of which are communicatively coupled. The spread spectrum modulationloop 1130 modulates the standard curve to generate a P-sequence ofvalues, which are then used to generate a desired frequency profile. Inone embodiment, the spread spectrum modulation loop 1130 is analogous tothe frequency spreading control pattern generation system 300 of FIG.3B, and the spread spectrum modulator 700 of FIG. 7.

The control circuit 1110 produces a plurality of input signals that isscalable for generating any type of frequency profile. For example, theplurality of input signals is capable of generating a standard curvethat is linear, in one embodiment. In another embodiment, the pluralityof input signals is capable of generating a standard curve that isnon-linear.

The control circuit 1110 outputs the plurality of input signals. Morespecifically, the frequency synthesizer 1100A of FIG. 11A produces astandard curve that is linear in shape. This is because the controlcircuit 1110 generates input signals in the plurality of input signalsthat exhibit a constant slope value. As such, the absolute value of theslope does not change.

However, the sign of the slope value may change. That is, in one inputsignal, the slope value is a positive constant value 1117. In addition,in another input signal of the plurality of input signals, the slopevalue is a negative constant value 1119.

As shown in FIG. 1100A, the control circuit 1110 comprises a multiplexer1115 for selecting the proper slope value, either the positive slopevalue 1117, or the negative slope value 1119, when the absolute value ofthe slope is a constant. The direction 1118 of the slope instructs themultiplexer 1115 to select either the positive slope value 1117, or thenegative slope value 1119.

As such, the output of the control circuit 1110 is the plurality ofinput signals that is arranged in a sequence. Each of the plurality ofinput signals comprises a slope and direction of the slope. That is,each of the input signals either is a positive slope value 1117, or anegative slope value 1119. In other words, each of the slopes in theplurality of input signals comprises a constant slope value. Each of theplurality of input signals also comprises a direction of the slope,wherein the direction of the slope varies between input signals, in oneembodiment.

The plurality of input signals is sent to an accumulator 1120, whichgenerates a standard curve. The standard curve is input into the spreadspectrum modulation loop 1130. The spread spectrum modulation loop 1130modulates the standard curve to generate a P-sequence of values thatconsists of feedback loop divider information. More specifically, theP-sequence of values is input into a divider of the phase-locked loop1140 of the frequency synthesizer 1110A to generate a desired frequencyprofile f_(VCO), as described previously. Furthermore, the spreadspectrum modulation loop can produce control signal sequence containingmultiple signals, which is defined as control state.

As shown in FIG. 11A, the accumulator 1120 comprises an adder 1123 and aregister 1125. The accumulator sums the plurality of input signals inorder to generate a standard curve.

In particular, for each cycle, the accumulator receives an input signalfrom the control circuit 1110 at an adder 1123. The input signal is partof the plurality of input signals delivered in sequence. The accumulatorreceives one input signal in the sequence per cycle.

More specifically, the adder 1123 sums the received input signal and apreviously summed value of received input signals to generate a currentsummed value, y, of received input signals. The previously summed valueof received input signals is received by the adder from the register1125 through a loop.

The current summed value of received input signals is then stored in theregister 1125. The current summed value of received input signals in theregister can then be provided through the loop back to the adder in thenext cycle as the previously summed value of received input signals. Forinstance, in the next cycle, the loop in the accumulator 1120 sends thesummed value of received input signals stored in the register 1125 backto the adder 1123, for use as the previously summed value of receivedinput signals.

In addition, the output of the accumulator 1120 is the current summedvalue, y. The current summed value, y, forms part of the standard curvethat is sent to the spread spectrum modulation loop 1130. That is, thesequence of values, y, that is output by the accumulator 1120 forms thestandard curve that is input to the spread spectrum modulation loop1130.

Thereafter, the spread spectrum modulation loop 1130 modulates thestandard curve to generate a P-sequence of values that are used togenerate the desired frequency profile. More particularly, theP-sequence of values is delivered to a divider of the phase-locked loop1140.

In embodiments of the present invention, the frequency synthesizer iscapable of tracking the standard curve at the output of the phase-lockedloop 1140. That is, if the standard curve is a linear curve, thegenerated frequency profile, f_(VCO), at the output of the phase-lockedloop will also be linear as it closely tracks the standard curve. Inaddition, if the standard curve is a non-linear curve, then thegenerated frequency profile, f_(VCO), at the output of the phase-lockedloop will also be non-linear as it closely tracks the standard curve.

In one embodiment, the standard curve is repeatable. That is, pluralityof input signals comprises a repeatable sequence. As such, the pluralityof input signals that are input to the spread spectrum modulation loop1130 will generate a P-sequence that generates a repeatable frequencyprofile at the output, f_(VCO), of the phase-locked loop 1140.

In another embodiment, the standard curve is non-repeatable. That is,the plurality of input signals comprises a non-repeatable sequence. Assuch, the plurality of input signals that are input to the spreadspectrum modulation loop 1130 will generate a P-sequence that generatesa non-repeatable frequency profile, f_(VCO), at the output of thephase-locked loop 1140.

In still another embodiment, the start condition of the frequencysynthesizer is zero. That is, the register 1125 holds a value of zero.In another embodiment, the register 1125 holds a non-zero value for thestart condition.

FIG. 11B is a block diagram of a frequency synthesizer 1100B thatimplements first order accumulation to generate a non-linear standardcurve that is further modulated to generate a frequency profile, inaccordance with one embodiment of the present invention. The frequencysynthesizer is capable of performing spread spectrum synthesis whengenerating a P-sequence of values used in a phase-locked loop of thefrequency synthesizer, in accordance with one embodiment of the presentinvention.

In one embodiment, the frequency synthesizer 1100B is analogous to thefrequency synthesizer 1100A of FIG. 11A. As such, it is intended thatsimilarly numbered elements of FIGS. 11A and 11B perform similarfunctions.

The frequency synthesizer 1100B comprises a system for modulating asignal to generate a standard curve. As shown in FIG. 11B, the frequencysynthesizer 1100B comprises a control circuit 1150, an accumulator 1120,a spread spectrum modulation loop 1130, and a phase-locked loop 1140,all of which are communicatively coupled. In summary, the spreadspectrum modulation loop 1130 modulates the standard curve outputted bythe accumulator 1120 to generate a P-sequence of values, which are thenused to generate a desired frequency profile.

As shown in FIG. 11B, the control circuit 1110 produces a plurality ofinput signals that is scalable for generating any type of frequencyprofile. For instance, in the present embodiment, the plurality of inputsignals is used to generate a standard curve that is non-linear.

In particular, the control circuit 1150 outputs the plurality of inputsignals. Specifically, the control circuit 1150 comprises a slopegenerator for generating the plurality of input signals that exhibit avarying slope. As such, the absolute value of the slope values betweeninput signals can change, in one embodiment. More particularly, theslope is capable of varying between input signals. Because of thevarying slope for the input signals, the frequency synthesizer 1100B ofFIG. 11B produces a standard curve that is non-linear in shape, in oneembodiment.

In one embodiment, the slope generator 1153 comprises an RC circuit thatvaries the slope between input signals. As such, the RC circuit is ableto generate a repeatable pattern that is used as slope values for theinput signals. In other embodiments, other means for generating thevarying slope values are implemented, such as a look-up tables of slopevalues, by calculation, etc.

In addition, the control circuit 1150 also comprises a directiongenerator 1155. Specifically, the direction generator 1155 generates asign of the slope value for the input signal. In one embodiment, theslope value for an input signal is a positive value. In anotherembodiment the slope value for an input signal is a negative value. Moreparticularly, the sign of the slope values is capable of varying betweeninput signals.

As such, the output of the control circuit 1150 is the plurality ofinput signals that is arranged in a sequence. Each of the plurality ofinput signals comprises a slope and direction of the slope. That is,each of the input signals comprises a variable slope value and adirection (e.g., positive or negative) of the slope value. In otherwords, each of the input values comprises a slope and direction, whereinthe slope and direction both are capable of varying between inputsignals, in one embodiment.

As previously described, the plurality of input signals is sent to theaccumulator 1120, which generates a non-linear standard curve, in thepresent embodiment. The standard curve is input into the spread spectrummodulation loop 1130, which modulates the standard curve to generate aP-sequence of values. The P-sequence is input into a divider of thephase-locked loop 1140 of the frequency synthesizer 1100B to generate adesired frequency profile, f_(VCO).

In embodiments of the present invention, the frequency synthesizer iscapable of tracking the standard curve at the output of the phase-lockedloop 1140. That is, since in the present embodiment the standard curveis a non-linear curve, the generated frequency profile, f_(VCO), at theoutput of the phase-locked loop 1140 will also be non-linear as itclosely tracks the standard curve.

Also, as previously described, the standard curve is repeatable in oneembodiment. As such, the standard curve that is input to the spreadspectrum modulation loop 1130 will generate a repeatable frequencyprofile at the output, f_(VCO), of the phase-locked loop. In anotherembodiment, the standard curve is non-repeatable. That is, the pluralityof input signals comprises a non-repeatable sequence. As such, thestandard curve that is input to the spread spectrum modulation loop 1130will generate a P-sequence that generates a non-repeatable frequencyprofile, f_(VCO), at the output of the phase-locked loop 1140. Forexample, this non-repeating frequency profile is used in communicationdevices implementing encryption.

FIG. 12A is a flow chart 1200A illustrating steps in a method formodulation that implements first order accumulation to generate astandard curve that is further modulated to generate a frequencyprofile, in accordance with one embodiment of the present invention. Inone embodiment, the method of flow chart 1200A is capable of performingfractional-N synthesis when generating a P-sequence of values used forgenerating a frequency profile in a frequency synthesizer.

At 1210, the present embodiment receives a plurality of input signals.Each of the plurality of input signals comprises a slope value and adirection (positive or negative) of the slope value. The plurality ofinput signals is scalable for generating any type of frequency profile(e.g., linear, non-linear, etc.), in one embodiment.

In one embodiment, the slope values between input signals are keptconstant. That is, the slopes of the plurality of input signals isconstant. The present embodiment varies the directions between inputsignals of the plurality of input signals. That is, even between twoinput signals, the direction may change. As such, one input signal maybe a positive slope value, while the next input signal may be a negativeslope value. As a result, the generated frequency profile will belinear.

In another embodiment, the slope values vary between input signals ofthe plurality of input signals. That is, the absolute value of slopevalues between input signals can vary and be different. In addition, thepresent embodiment varies the directions between input signals of theplurality of input signals. That is, between two input signals, thedirection (positive or negative) may change. As such, one input signalmay be a positive slope of a first slope value, while the next inputsignal may be a negative slope of a second slope value.

At 1220, the present embodiment accumulates the plurality of inputsignals to generate a standard curve. The standard curve is used by aspread spectrum modulation loop to generate a P-sequence of values thatconsists of feedback loop divider information.

At 1230, the present embodiment modulates the standard curve to generatea spread spectrum frequency profile. More particularly, the presentembodiment modulates the standard curve to generate a P-sequence. TheP-sequence is used by a feedback divider of a phase-locked loop forgenerating the spread spectrum frequency profile, as previouslydescribed in relation to FIGS. 11A and 11B.

FIG. 12B is a flow diagram 1200B illustrating steps in a method forgenerating the standard curve from the plurality of input signals, inaccordance with one embodiment of the present invention. FIG. 12B is afurther description of 1220 of FIG. 12A, in one embodiment.

At 1221, the present embodiment receives an input signal. The inputsignal is part of a sequence that defines the plurality of inputsignals.

At 1223, the present embodiment sums the input signal with a previouslysummed value of received input signals to generate a current summedvalue of received input signals. As such, with each additional inputsignal of the sequence that is received, the present embodimentaccumulates the input signal along with the previously summed value ofthe received input signals, in order to generate a current summed value.Each of the current summed values in sequence form the standard curve.

At 1225, the current summed value of the received input signal isstored. As such, the current summed value of received input signals canbe retrieved for use in forming the standard curve.

Additionally, at 1227, the current summed value of received inputsignals is used in calculating future summed values. That is, thecurrent summed value is fed back to 1260 in the next cycle to be summedwith the next input signal.

Higher Order Accumulation for Generating a Standard Curve that isFurther Modulated to Generate a Desired Frequency Profile

FIG. 13A is a block diagram of a spread spectrum frequency synthesizer1300A including a high or higher order accumulator block for generatinga non-linear standard curve, in accordance with one embodiment of thepresent invention. The terms high and higher order can be usedinterchangeably. The frequency synthesizer is capable of performingspread spectrum synthesis when generating a P-sequence of values used ina phase-locked loop of the frequency synthesizer, in accordance with oneembodiment of the present invention.

The frequency synthesizer 1300A comprises a system for modulating asignal to generate a standard curve 1325. As shown in FIG. 13A, thefrequency synthesizer 1300A comprises a control circuit 1310, a higherorder accumulator 1320, a spread spectrum modulation loop 1330, and aphase-locked loop 1340, all of which are communicatively coupled.

In particular, the spread spectrum modulation loop 1130 modulates thestandard curve 1325 to generate a P-sequence of values 1335, which arethen used to generate a desired frequency profile, f_(VCO). In oneembodiment, the spread spectrum modulation loop 1130 is analogous to thefrequency spreading control pattern generation system 300 of FIG. 3B,and the spread spectrum modulator 700 of FIG. 7, for example.

The control circuit 1310 generates a plurality of input signals that isscalable for generating any type of frequency profile. That is, thecontrol circuit 1310 outputs the plurality of input signals. Forexample, the plurality of input signals is capable of generating astandard curve 1325 that is non-linear, in one embodiment.

In particular, the control circuit 1310 comprises control logic 1315 anda multiplexer 1317 for generating the plurality of input signals, inaccordance with one embodiment. It is to be understood that otherembodiments of the control circuit 1310 are capable of generating theplurality of input signals.

The control logic 1315 generates and delivers delta signals, directionsignals, load condition signals, and value signals. The control logic1315 also receives a period signal, and intermediary output signals(e.g., y₁, y₂, . . . , y_(n)) that are fed back from the higher orderaccumulator 1320, as will be described below.

The period signal indicates how many phases define the standard curve1325. In particular, FIG. 15 is a graph illustrating the four phases ofa standard curve, 1325. As shown in FIG. 15, the standard curve 1325 isdefined by four phases. The first phase 1510 begins at point A and endsat the positive peak denoted by point B. The second phase 1520 begins atpoint B and ends at the zero crossover at point C. The third phasebegins at point C and ends at the negative peak at point D. The fourthphase beings at point D, and ends at the zero cross-over at point E.

As shown in FIG. 15, each phase may be broken down into a plurality ofcycles, each of which produces a value y used in sequential order toproduce the standard curve 1325. For instance, each of the four phasesof the standard curve 1325 may be defined by 100 cycles. As such, thefirst phase is defined by cycles 0-99. The second phase is defined bycycles 100-199. The third phase is defined by cycles 200-299. The fourthphase is defined by cycles 300-399.

Returning now to FIG. 13A, the control logic 1315 comprises a slopegenerator 1316 and a direction generator 1319, in accordance with oneembodiment. In particular, the slope generator 1316 generates the slopevalue, delta, for the plurality of input signals. The directiongenerator 1319 generates the direction assigned to a corresponding slopevalue in a corresponding input signal.

In one embodiment, the slope value, delta, is constant. As such, theinput signal, m, for a particular cycle that is output from the controlcircuit 1310 would be either the positive delta value 1301, or thenegative delta value 1302, where the absolute value of the slope isdelta.

The direction signal 1303 provided by the direction generator 1319instructs the multiplexer 1317 to select either the positive delta value1301 or the negative slope value 1302. As such, the sign of the slopevalue, delta, may change. That is, between input signals, the direction,or sign, of the slopes may be different. For instance, in one cycle, theinput signal, m, may be positive delta 1301. In the following cycle, theinput signal, m, may be negative delta 1302.

In another embodiment, the slope value, delta, is varying. That is, theslope value, delta, may change between input signals. As such, the slopegenerator 1316 generates the slope value, delta, for each input signal,or cycle. Thereafter, the slope generator 1316 delivers both thepositive delta 1301, and the negative delta 1302 to the multiplexer1317. Selection of either the positive delta 1301 or the negative delta1302 depends on the direction signal 1303 generated by the directiongenerator 1319 for that input signal, or cycle.

As such, the output of the control circuit 1310 is the plurality ofinput signals that is arranged in a sequence. Each of the plurality ofinput signals comprises a slope and a direction of the slope. That is,each of the input signals either is a positive delta 1301, or a negativedelta 1302. Each of the plurality of input signals also comprises adirection of the slope for selecting between the positive delta 1301 andthe negative delta 1302, wherein the direction of the slope variesbetween input signals, in one embodiment.

The plurality of input signals is sent to a higher order accumulatorblock 1320. In particular, the higher order accumulator block 1320receives the plurality of input signals from the control circuit 1310.The higher order accumulator block 1320 comprises at least twoaccumulators, in one embodiment. More specifically, the higher orderaccumulator block 1320 sums the plurality of input signals to generate astandard curve 1325 that is non-linear, in one embodiment.

As shown in FIG. 13A, the logic circuit 1310 generates and deliver loadcondition signals and value signals to the higher order accumulator1320. The load condition signal 1311 is associated with a correspondingvalue signal 1312 that comprises a load value. The load condition signal1311 instructs the higher order accumulator to load the load value andis used for controlling the shape of the standard curve, as will befurther described below.

The spread spectrum modulation loop 1130 receives the standard curve1325. In particular, the spread spectrum modulation loop 1330 modulatesthe standard curve 1325 to generate a P-sequence 1335 of values thatconsists of feedback loop divider information. The P-sequence 1335 ofvalues in one embodiment is a spread spectrum control sequence. Morespecifically, the P-sequence 1335 of values is input into a divider ofthe phase-locked loop 1340 of the frequency synthesizer 1110A togenerate a desired frequency profile f_(VCO), as described previously.

FIG. 13B is a block diagram of a higher order accumulator block 1320Acomprising a plurality of accumulators coupled in series for generatinga non-linear standard curve that is modulated to generate a frequencyprofile, in accordance with one embodiment of the present invention. Inone embodiment, the higher order accumulator block 1320A of FIG. 13Bprovides further details to the higher order accumulator block 1320 ofFIG. 13A.

In particular, the higher order accumulator block 1320A of FIG. 13Bcomprises at least two accumulators in series. For example, in oneembodiment, the higher order accumulator block 1320 comprises a firstaccumulator that is coupled in series with a second accumulator.

In one embodiment, the first accumulator receives the plurality of inputsignals, and generates a first plurality of outputs. The secondaccumulator receives the first plurality of outputs and generates asecond plurality of outputs. In one embodiment, the second plurality ofoutputs comprises the standard curve 1325.

In another embodiment, the higher order accumulator block 1320Acomprises n accumulators that are coupled in series, where n is equal toor greater than two. In particular, as shown in FIG. 13B, the higherorder accumulator block 1320A comprises a first accumulator 1321 thatreceives a plurality of input signals from the control circuit 1310.

More specially, in one cycle, the first accumulator 1321 receives aninput signal, m, from the control circuit 1310. The first orderaccumulator sums the plurality of input signals and generates a firstplurality of output signals. That is, in the present cycle, the firstaccumulator 1321 generates a first output, y₁.

In addition, the higher order accumulator block 1320A comprises a secondaccumulator 1322 coupled to the first accumulator 1321 in series. In onecycle, the second accumulator 1322 receives the first output, y₁, andsums the first output with previously received first outputs to generatea second output, y₂. That is, over many cycles, the second orderaccumulator sums the plurality of inputs that comprises a plurality offirst outputs, y₁. As such, the second order accumulator 1322 sums theplurality of received inputs, y₁, and generates a second plurality ofoutputs.

As shown in FIG. 13B, the higher order accumulator includes naccumulators coupled in series. The n^(th) accumulator 1323 receives theoutput from the n−1^(th) accumulator. In particular, the n^(th)accumulator receives the n−1^(th) output and generates the n_(th)output, y_(n). The y_(n) sequence of outputs from the n^(th) accumulator1323 forms the standard curve 1325 over many cycles.

In one embodiment, the higher order accumulation block 1320A of FIG. 13Bis capable of loading conditions at each of the accumulators forcontrolling the shape of the standard curve 1325. In one embodiment,each of the accumulators can load conditions independently, as directedby the control circuit 1310. For example, the description of loadingconditions for accumulator 1390 of FIG. 13D is equally applicable to theaccumulators of the higher order accumulator block 1320A of FIG. 13D.That is, a load signal can instruct a corresponding register to load anassociated value.

Load conditions are asserted at critical points in the formation of thestandard curve 1325. For example, in one embodiment, load conditions areasserted when the standard curve changes phases in a period. In anotherembodiment, load conditions are asserted mid-phase. As such, theasserted load conditions are asserted to better shape the standard curve1325 at any point in the standard curve 1325.

FIG. 13C is a block diagram of a higher order accumulator block 1320Bcomprising a plurality of accumulators coupled in series for generatinga non-linear standard curve that is modulated to generate a frequencyprofile, in accordance with one embodiment of the present invention. Inone embodiment, the higher order accumulator block 1320B of FIG. 13Cprovides further details to the higher order accumulator block 1320 ofFIG. 13A.

In particular, the higher order accumulator block 1320B of FIG. 13C iscoupled to the control circuit 1310 of FIG. 13A. The control circuit1310 generates a plurality of input signals that is scalable to afrequency profile. Each of the input signals comprises a slope and adirection of the slope. More specifically, the higher order accumulatorblock 1320B receives a plurality of input signals (e.g., an m sequence)for summing a non-linear curve with a linear curve to generate astandard curve 1325 that is non-linear, in accordance with oneembodiment of the present invention.

In accordance with one embodiment of the present invention, a spreadspectrum modulation loop receives the standard curve 1325. The spreadspectrum modulation loop comprises a phase-locked loop, and modulatesthe standard curve 1325 to generate a P-sequence in order to generate adesired frequency profile that tracks the standard curve.

As shown in FIG. 13C, the higher order accumulator block 1320B comprisesa first path 1350 and a second path that comprise an accumulator 1360.The first path 1350 comprises at least two accumulators coupled inseries. More specifically, the first path 1350 receives a firstplurality of input signals (e.g., an m sequence) from the controlcircuit 1310, and sums the first plurality of input signals to generatea non-linear curve y″.

As shown in FIG. 13C, the first path 1350 comprises n accumulators thatare coupled in series, where n is equal to or greater than two. Inparticular, as shown in FIG. 13C, the first path 1350 comprises a firstaccumulator 1351 that receives a plurality of input signals (e.g., msequence) from the control circuit 1310.

More specifically, in one cycle, the first accumulator 1351 receives aninput signal, m, from the control circuit 1310. In the present cycle,the first accumulator 1321 generates a first output, y₁. Over manycycles, the first accumulator 1321 generates a y₁ sequence.

In addition, the first path 1350 comprises a second accumulator 1352coupled to the first accumulator 1351 in series. In one cycle, thesecond accumulator 1322 receives the first output, y₁, and sums thefirst output with previously received first outputs to generate a secondoutput, y₂. That is, over many cycles, the second accumulator 1352 sumsthe received inputs that comprise a y₁ sequence. As such, the secondaccumulator 1352 sums the y₁ sequence, and generates a second pluralityof outputs, y₂ sequence.

As shown in FIG. 13C, the first path comprises an n^(th) accumulator1353. The n^(th) accumulator 1353 receives the output from the n−1^(th)accumulator. In particular, the n^(th) accumulator 1353 receives then−1^(th) output and generates the n^(th) output, y_(n). The y_(n)sequence of outputs from the n^(th) accumulator 1353 forms thenon-linear curve, y″ over many cycles.

The second path comprises another accumulator block 1360. Theaccumulator 1360 receives a second plurality of input signals from thecontrol circuit 1310 and sums the second plurality of input signals togenerate a linear curve, y′. In one embodiment, the first plurality ofinput signals and the second plurality of input signals from the controlcircuit 1310 is substantially similar. As such, the first accumulator1351 and the accumulator 1360 would receive the same input signal, m,per cycle, and generate the same output, y₁.

In one embodiment, the accumulators 1351, 1352, 1353, and 1360 aresimilar in configuration with the accumulator 1390 of FIG. 13D. As such,the functions and operations of the accumulator 1390 are applicable tothe accumulators of the higher order accumulator block 1320B of FIG.13C.

As shown in FIG. 13B, the higher order accumulator block 1320B alsocomprises an adder 1370. The adder 1370 is coupled to the first path1350 and the accumulator 1360. Specifically, the adder 1370 sums the y″sequence that forms the non-linear curve that is output from the firstpath 1350 with the y′ sequence that forms the linear curve that isoutput from the accumulator 1360 from the second path. As such, theadder 1370 generates the y sequence that forms the standard curve 1325.

In particular, the accumulator 1360 of the second path acts to averageout and smooth the shape of the non-linear curve, y″ of the first path1350. Without the contribution of the accumulator 1360, the non-linearcurve, y″, may be too slow at the beginning of the first phase (e.g.,point A of FIG. 15), and may climb too fast when approaching the peak atthe beginning of the second phase (e.g., point B of FIG. 15).

As such, the linear curve y′ would increase the output values of thestandard curve 1325 at the beginning of the first phase. In addition,the linear curve y′would decrease the output values of the standardcurve 1325 when approaching the beginning of the second phase.

In one embodiment, the higher order accumulation block 1320B of FIG. 13Cis capable of loading conditions at each of the accumulators forcontrolling the shape of the standard curve 1325. In one embodiment,each of the accumulators can load conditions independently, as directedby the control circuit 1310. For example, the description of loadingconditions for accumulator 1390 of FIG. 13D is equally applicable to theaccumulators of the higher order accumulator block 1320B of FIG. 13C.That is, a load signal can instruct a corresponding register to load anassociated value.

Load conditions are asserted at critical points in the formation of thestandard curve 1325. For example, in one embodiment, load conditions areasserted when the standard curve changes phases in a period. In anotherembodiment, load conditions are asserted mid-phase, as previouslydescribed. As such, the asserted load conditions are asserted to bettershape the standard curve 1325 at any point in the standard curve 1325.

For purposes of clarity and brevity, FIG. 13D is a block diagram of anexemplary accumulator 1390 used within the higher order accumulator 1320of FIG. 13A, in accordance with one embodiment of the present invention.For instance, each of the accumulators in the higher order accumulatorblock 1320 of FIG. 13A, or the higher order accumulator block 1320A ofFIG. 13B is analogous to the accumulator 1390.

In particular, the accumulator 1390 comprises an adder 1391 and aregister 1392, in accordance with one embodiment of the presentinvention. More specifically, the adder 1390 receives an input 1395. Inone embodiment, the adder 1391 may receive an input, m, as input 1395,from the control circuit 1310. In another embodiment, the adder 1390 mayreceive an input, y_(x), as input 1395, from a previous accumulatorcoupled in series. For instance, the second accumulator 132 of FIG. 13Bmay comprise the adder 1391 and receive the input, y₁, from the firstaccumulator 1321.

The adder sums the input 1395 and a previously summed value of receivedinputs to generate a current summed value of received inputs.

A register 1392 is coupled to the adder 1391. The register stores thecurrent summed value of received inputs. In addition, in one embodiment,the current summed value of received inputs comprises an output signalthat is used for one cycle of the standard curve 1325, if theaccumulator is the n^(th) accumulator. In another embodiment, thecurrent summed value is used as another input for a followingaccumulator.

In addition, the accumulator 1390 comprises a feedback loop 1393. Thefeedback loop 1393 sends the previously summed value of received inputs,that were previously stored in the register back to the adder 1391. Thatis, in one cycle, the accumulator 1390 receives the input 1395, sums theinput with the previously summed value of received inputs stored in theregister 1392 to generate a current summed value of received inputs, andstores the current summed value of received inputs into the register1392.

In one embodiment, the higher order accumulation block 3120 of FIG. 13Ais capable of loading conditions at each of the accumulators forcontrolling the shape of the standard curve 1325. In one embodiment,each of the accumulators can load conditions independently, as directedby the control circuit 1310. For purposes of clarity and brevity, thefollowing description of the accumulator 1390 of FIG. 13D for receivingload conditions is applicable to loading conditions in all of theaccumulators in the higher order accumulator 1320 of FIGS. 13A, 13B, and13C.

As shown in FIG. 13D, the register 1392 is instructed by the controllogic 1315 of the control circuit 1310 to receive a load condition usingcontrol signals. That is, the load signal 1396 instructs the register1392 whether to load a condition, or to receive the current summed valueof received inputs from the adder 1391. Specifically, if the load signalis asserted, then the register 1392 loads the corresponding value 1397that is provided by the control circuit 1310. On the other hand, if theload signal is not asserted, then the register 1392 ignores the value1392 and loads or stores the current summed value of received inputsfrom the adder 1391.

Load conditions are asserted at critical points in the standard curve1325. For example, in one embodiment, load conditions are asserted whenthe standard curve changes phases in a period. Referring to FIG. 15,load conditions are asserted at corresponding accumulators of the higherorder accumulator block 1320 when the standard curve reaches points A,B, C, and D for each period generated for the standard curve 1325.

For instance, in a higher order accumulator block 1320 that includesaccumulators in series, for a constant input m that is positive throughthe first phase, the sequential output of y_(n) that generates thestandard curve 1325 will start out slowly at point A, then quickly rampup exponentially until reaching point B. Asserting load conditions atpoints A and B will help shape the standard curve so that the standardcurve increases more quickly past point A, and can set the conditionsfor the accumulators such that at point B the standard curve enters thenext phase correctly.

In addition, in another embodiment, load conditions are assertedmid-phase (e.g., between points A and B). For example, without loadconditions, the shape of the standard curve 1325 may increase tooquickly when approaching point B. As such, a mid-phase load conditionmay be asserted to better shape the standard curve 1325 at any point inthe standard curve 1325.

In still another embodiment, a reset condition is an example of one loadcondition. That is, at reset, the starting load conditions for eachaccumulator in the higher order accumulator block 1320 is asserted. Forinstance, all the registers in the accumulators in the higher orderaccumulator block 1320 can be reset to zero.

FIG. 14 is a flow chart 1400 illustrating steps in a method formodulation that implements higher order accumulation to generate afrequency profile, in accordance with one embodiment of the presentinvention. In one embodiment, the method of flow chart 1400 is capableof performing fractional-N synthesis when generating a P-sequence ofvalues used for generating a frequency profile in a frequencysynthesizer.

At 1410, the present embodiment receives a plurality of input signals.Each of the plurality of input signals comprise a slope value and adirection (positive or negative) of the slope value. The plurality ofinput signals is scalable for generating any type of frequency profile(e.g., linear, non-linear, etc.), in one embodiment.

In one embodiment, the slope values between input signals are keptconstant. That is, the slopes, deltas, of the plurality of input signalsare constant. The present embodiment varies the directions between inputsignals of the plurality of input signals. That is, even between twoinput signals, the direction may change. As such, one input signal maybe a positive slope value, while the next input signal may be a negativeslope value.

In another embodiment, the slope values vary between input signals ofthe plurality of input signals. That is, the absolute value of slopevalues between input signals can vary and be different.

At 1420, the present embodiment, accumulates the plurality of inputsignals through at least two accumulation stages to generate a standardcurve. In particular, in one embodiment, the standard curve that isgenerated is non-linear. The standard curve is used by a spread spectrummodulation loop to generate a P-sequence of values that consists offeedback loop divider information.

In one embodiment, the present embodiment, accumulates the plurality ofinput signals through at least two accumulation stages that arecommunicatively coupled in series. In particular, at each of theaccumulation stages, the accumulation stage receives an input fromeither the plurality of input signals, or from a previous accumulationstage.

Thereafter, the input is summed with a previously summed value ofreceived inputs to generate a current summed value of received inputs.As such, with each additional input of a sequence that is received, thepresent embodiment accumulates the input along with a previously summedvalue of inputs, in order to generate a current summed value. Thecurrent summed value comprises an output that can be used as thestandard curve or as another input for a following accumulation stage.

In addition, the present embodiment, stores the current summed value ofreceived inputs for use in calculating future summed values. Forinstance, the current summed value is used fed back in the next cycle tobe summed with the next input that is received by the correspondingaccumulator.

In another embodiment, the output from the two or more accumulatorscoupled in series is summed with a linear curve that is generated from asingle accumulator. That is, the present embodiment, sums a non-linearcurve generated from the accumulators coupled in series with a linearcurve from the single accumulator in order to generate the standardcurve that is also non-linear.

At 1430, the present embodiment modulates the standard curve to generatea spread spectrum frequency profile. More particularly, the presentembodiment, modulates the standard curve to generate the P-sequence. TheP-sequence is used by a feedback divider of a phase-locked loop forgenerating the spread spectrum frequency profile, as previouslydescribed in relation to FIGS. 13A, 13B, and 13C.

In still another embodiment, load conditions are asserted in theaccumulation stages. Specifically, the asserted load conditions shapethe output curve to generate a desired standard curve. The loadconditions are independently asserted at each of the accumulationstages, in one embodiment.

Spread Spectrum Frequency Synthesizer with Improved Frequency Shape forSpread Spectrum Modulation

Accordingly, embodiments of the present invention provide for thegeneration of improved frequency profiles by adjusting the length of astandard curve used to modulate an input signal when performing spreadspectrum modulation. The term “length of a standard curve” is the numberof points used in one modulation cycle, a convention from look-up tablestyle modulation where length of a standard curve usually refers tonumber of points in one standard curve cycle.

FIGS. 16 and 17 in combination with the previously discussed Figures,and in particular, FIGS. 1A, 1B, 1C, 2, 3A, 3B, 11A and 11B illustrateembodiments of the present invention in which a length of a standardcurve is manipulated in such a manner to improve the frequency shape ofthe standard curve when performing spread spectrum modulation. Inparticular, FIGS. 16 and 17 are flow charts illustrating steps incomputer implemented methods for adjusting the length of the standardcurve to provide for improved EMI reduction when performing spreadspectrum modulation.

Referring now to FIG. 16, a flow diagram 1600 is shown illustratingsteps in a computer implemented method for sampling a standard curve ina spread spectrum modulator such that critical points of the standardcurve are captured, in accordance with one embodiment of the presentinvention.

At 1610, a standard curve is generated. In one embodiment, the standardcurve is determined by software from a function. The software generatesvalues representing the standard curve for inclusion into a look-uptable, for example. In another embodiment, the standard curve isgenerated by hardware. That is, values representing the standard isdetermined through combinational logic for inclusion. For instance,FIGS. 11A, 11B, 12A, 12B, 13A, 13B, 13C, 13D, 14, and 15 and theircorresponding discussions provide means for generating the standardcurve. The standard curve is associated with a frequency or perioddefining a shape of the standard curve. This frequency or period becomesa modulation frequency or period when modulating the VCO frequency.

In one embodiment, the standard curve is repeatable with a shape that isrepeatable every four phases of equal length. For instance, the standardcurve is a non-linear curve (e.g., a Hershey Kiss curve in FIG. 15 withfour phases points A to B, points B to C, points C to D, and points D toE of equal length). In another embodiment, the standard curve isrepeatable with a shape that is repeatable every two phases. Forinstance, the standard curve is a linear (e.g., triangular) curve. Inother embodiments, the standard curve has an average value of zero. Instill other embodiments, the standard curve is periodic. In otherembodiments, the standard curve is non-periodic, or random.

The standard curve is analogous to the input modulation signal MS305 inFIG. 3B, in one embodiment. Additionally, the standard curve isanalogous to the standard curve that is output from the accumulator1120, and input to the spread spectrum modulation loop 1130 of FIGS. 11Aand 11B. It is appreciated that the input modulation signal or standardcurve can have a variety of different configurations, including standardand/or non-standard schemes (e.g., patterns, curves, etc.). As such, thestandard curve modulates an input signal (e.g., input clock signalgenerated by the oscillator 211) to generate a spread spectrum offrequencies with reduced amplitude and spreading of bandwidth, inaccordance with one embodiment of the present invention.

At 1620, the present embodiment samples the standard curve at a samplingfrequency. In other words, the standard curve is modulated for use inthe spread spectrum frequency modulator of embodiments of the presentinvention. In particular, in one embodiment, the standard curve issampled at a sampling frequency that comprises a frequency of a phasefrequency detector (PFD) in a PLL loop of the spread spectrum frequencymodulator. In another embodiment, the standard curve is sampled at asampling frequency that comprises a frequency of a P-counter in a PLLloop of the spread spectrum frequency modulator. As such, as shown inFIG. 1B, the frequency of the PFD 221 is analogous to the sample rate,or the modulation frequency of the standard curve. Furthermore, as shownin FIGS. 11A and 11B, the frequency of the PFD 221 is equal to thefrequency of the voltage controlled oscillator (f_(VCO)) divided by thefeedback loop divide value (also referred to as “P”) within the feedbackloop divider 224 of FIG. 1B.

At 1630, the present embodiment adjusts a length of the standard curvesuch that critical points of the standard curve are captured. The lengthdefines the number of points of the standard curve that are sampled inone modulation cycle. In one embodiment, the length is an integer value.In another embodiment, the length is determined by dividing the samplingfrequency (f_(samping)) by the modulation frequency (f_(m)), asdescribed in Equation 1:1=f _(sampling) /f _(m)  (1)

As shown in Equation 1, the length (l) can be adjusted by adjusting thefrequency variables. In one embodiment, the length of the standard curveis adjusted by adjusting the modulation frequency (f_(m)) of thestandard curve. In another embodiment, the length of the standard curveis adjusted by adjusting the sampling frequency (f_(sampling)). In stillanother embodiment, the length of the standard curve is adjusted byadjusting the modulation frequency (f_(m)) and the sampling frequency(f_(sampling)). In embodiments of the present invention, the length (l)is determined to be an integer divisible by a value two, or value four,or by any integer, as will be described below.

In each of these embodiments, the goal is to determine a length (l) thatcaptures the critical points of the standard curve, in embodiments ofthe present invention. In accordance with one embodiment of the presentinvention, the length of the standard curve is adjusted such that thelength comprises an integer divisible by a value of four, when thestandard curve comprises a non-linear curve, whose shape is repeatableevery four phases, as is shown in FIG. 18A. In another embodiment, thelength of the standard curve is adjusted such that the length comprisesan integer divisible by a value of two, when the standard curvecomprises a linear curve, whose shape is repeatable every two phases.

FIG. 18A is a graph illustrating an example length of a standard curvethat is used for spread spectrum modulation with improved EMIperformance. As shown, FIG. 18A is a graph illustrating the propersampling of the non-linear standard curve, in accordance with oneembodiment of the present invention. The example of FIG. 18A is shown toillustrate the capture of critical points in a standard curve. While theembodiment of the present invention as shown in FIG. 18A is directed tothe adjusting of the length of a non-linear standard curve, otherembodiments of the present invention are well suited to adjusting thelength of a linear standard curve to capture critical points. That is,the critical points shown in FIG. 18A are illustrative of criticalpoints for a non-linear curve and a linear curve, in embodiments of thepresent invention.

As shown in FIG. 18A, the horizontal axis represents an index indicatingthe sampled points of the standard curve. The vertical axis indicatesthe normalized y value of the standard curve, between −1 and +1. Asdescribed before in relation to FIGS. 11A and 11B, the y value can bethe current value of generated by the accumulator 1120 and forms part ofthe standard curve that is sent to the spread spectrum modulation loop1130, in one embodiment. As such, the plurality of y values generatesthe standard curve.

In FIG. 1800A, the standard curve 1850 is represented by the solid line.Sample points of the standard curve 1850 are represented byopen-circles. Because of the proper length selected, critical points ofthe standard curve 1850 are captured, thereby giving a truerepresentation of the standard curve 1850. As shown in FIG. 18A, thelength of the standard curve 1850 is shown, wherein l=20. In accordancewith embodiments of the present invention, the length of a standardcurve that is non linear (e.g., standard curve 1850) is divisible by avalue of four. As such, with a length, l=20, the standard curve 1850 issampled twenty times over a period 1852.

In particular, in one embodiment, peaks of the standard curve arecaptured. For instance, isolation area 1854 and 1856 show peaks of theideal standard curve 1850 which are captured. Also, in anotherembodiment, zero cross-over points of the standard curve are captured.For instance, isolation areas 1855 and 1857 show open-circlesrepresenting zero cross-over points that are captured. This results inproper shaping of the ideal standard curve 1850 and improved performanceof EMI reduction.

FIG. 18E shows proper selection of the length for a non-linear curve. Aspreviously described, for a non-linear curve of four phases, the lengthshould achieve a ratio between the sampling frequency (f_(sampling)) andthe modulation frequency (f_(m)) that is divisible by a value of four,in accordance with one embodiment of the present invention. As shown inFIG. 18E, two lengths are shown for a standard curve (e.g., standardcurve 1850), wherein the lengths are able to capture the critical pointsin the standard curve. For example, the length, l=20, and the length,l=24, both capture the critical points (e.g., zero cross-over and peakpoints).

In particular, in accordance with embodiments, of the present invention,the length of the non-linear standard curve (e.g., standard curve 1850)is divisible by a value of four. As such, the plot of open-circlesrepresents the sampling of the standard curve when l=20. As such, with alength, l=20, the standard curve is sampled twenty times over a period1861. As shown in FIG. 18E, the critical zero cross-over points (e.g.,points 1863) and peak points (points 1864) are captured when l=20. Inaddition, the plot of open-squares represents the sampling of thestandard curve when l=24. As such, with a length, l=24, the standardcurve is sampled twenty-four times over a period 1862. As shown in FIG.18E, the critical zero cross-over points (e.g., points 1871) and thepeak points (e.g., points 1872) are captured when l=24.

On the other hand, in one technology, the length of the modulationfrequency as used in spread spectrum control pattern generation isdecided by performing an integer round up of the length based on themodulation frequency. This technique can result in the missing ofcritical sample points in the standard curve.

For instance, this technique for determining length can result in pointmissing of the standard shape. In particular, FIGS. 18B, 18C, and 18Dare graphs illustrating the poor sampling of the standard curve duringmodulation. In each of the FIGS. 18B, 18C, and 18D, improper lengths areimplemented for the modulation frequency of the standard curve,resulting in poor sampling of the standard curve. It is worse when thelength is relatively small. This results in poor modulation of thespread spectrum of the input signal and poor EMI performance of thespread spectrum frequency modulator.

For example, FIG. 18B is a graph illustrating the poor sampling of thestandard curve during modulation when the length is 21, in accordancewith one embodiment of the present invention. As shown in FIG. 18B, thehorizontal axis represents an index indicating the sampled points of thestandard curve. The vertical axis indicates the normalized y value ofthe standard curve, between −1 and +1. As described before in relationto FIGS. 11A and 11B, the y value can be the current value of generatedby the accumulator 1120 and forms part of the standard curve that issent to the spread spectrum modulation loop 1130, in one embodiment. Assuch, the plurality of y values generates the standard curve.

As shown in FIG. 1800B, the ideal curve of the standard curve 1820 isshown by the solid line. The length of the ideal standard curve 1820 isshown, where l=21 for sampling. The length of the ideal standard curve1820 is associated with the modulation frequency or sampling rate of theideal standard curve 1820. As such, with a length of 21, the idealstandard curve 1820 is sampled twenty-one times over a period 1822 ofthe ideal standard curve 1820.

The actual or true standard curve is represented by the open circles atselected points. Because of the improper length selected, the shape ofthe true standard curve does not match that of the ideal standard curve1820. For instance, isolation areas 1824 and 1826 show peaks of theideal standard curve 1820 which are not captured by the true standardcurve. This results in poor shaping of the ideal standard curve and poorperformance of EMI reduction.

This problem of point missing of the ideal standard curve is also shownfor various values of the length. For example, FIG. 18C is a graphillustrating the poor sampling of the standard curve during modulationwhen the length is 22. As shown in FIG. 18C, the ideal standard curve1830 is shown by the solid line. The true standard curve is representedby the plot connected by the open-circles. As such, with a length of 22,the ideal standard curve is sampled twenty-two times over a period 1832of the ideal standard curve. Because of the improper length selected,the shape of the true standard curve does not match that of the idealstandard curve 1830. For instance, isolation areas 1834 and 1836 showpeaks of the ideal standard curve 1830 which are not captured by thetrue standard curve. This results in poor shaping of the ideal standardcurve and poor performance of EMI reduction.

Additionally, FIG. 18D is a graph illustrating the poor sampling of thestandard curve during modulation when the length is 23. As shown in FIG.18D, the ideal standard curve 1840 is shown by the solid line. The truestandard curve is represented by the plot connected by the open-circles.As such, with a length of 23, the ideal standard curve 1840 is sampledtwenty-three times over a period 1842 of the ideal standard curve 1840.Because of the improper length selected, the shape of the true standardcurve does not match that of the ideal standard curve 1840. Forinstance, isolation areas 1844 and 1846 show peaks of the ideal standardcurve 1840 which are not captured by the true standard curve. Thisresults in poor shaping of the ideal standard curve and poor performanceof EMI reduction.

FIG. 17 is a flow diagram illustrating steps in a computer implementedmethod for sampling a standard curve in a spread spectrum modulator suchthat critical points of the standard curve are captured, in accordancewith one embodiment of the present invention.

At 1710, the present embodiment generates a standard curve. The standardcurve is associated with a modulation frequency defining a shape of thestandard curve. In embodiments of the present invention, the standardcurve is linear or non-linear. As described previously, the standardcurve is analogous to the input modulation signal MS305 in FIG. 3B.Additionally, the standard curve is analogous to the standard curve thatis output from the accumulator 1120, and input to the spread spectrummodulation loop 1130 of FIGS. 11A and 11B. It is appreciated that theinput modulation signal or standard curve can have a variety ofdifferent configurations, including standard and/or non-standard schemes(e.g., patterns, curves, etc.), as described previously. As such, thestandard curve modulates an input signal (e.g., input clock signalgenerated by the oscillator 211) to generate a spread spectrum offrequencies with reduced amplitude and spreading of bandwidth, inaccordance with one embodiment of the present invention.

In one embodiment, a target modulation frequency is determined formodulating the standard curve. The target modulation frequency typicallyis found within a range of frequencies. In one embodiment, the targetmodulation frequency is determined by the manufacturer.

At 1720, the present embodiment samples the standard curve at a samplingfrequency. In other words, the standard curve is modulated for use inthe spread spectrum frequency modulator of embodiments of the presentinvention. In particular, in one embodiment, the standard curve issampled at a sampling frequency that comprises a frequency of a phasefrequency detector (PFD) in a PLL loop of the spread spectrum frequencymodulator, as previously described. In another embodiment, the standardcurve is sampled at a sampling frequency that comprises a frequency of aP-counter in a PLL loop of the spread spectrum frequency modulator, aspreviously described. As such, as shown in FIG. 1B, the frequency of thePFD 221 is analogous to the sample rate.

At 1730, the present embodiment adjusts a length of the standard curvesuch that critical points of the standard curve are captured. Inparticular, the length is adjusted, such that the length comprises aninteger divisible by the value two, four or any other integer number,without remainder, depending on the shape of the standard curve. Afteradjusting the length, the sampled representation of the standard curveremains in a uniform pattern between periods, in one embodiment. Inanother embodiment, the length, as an integer, is adjusted to bedivisible by the value of four when the standard curve comprises anon-linear curve of four equal length phases. In another embodiment, thelength, as an integer, is adjusted to be divisible by two when thestandard curve comprises a linear curve.

For example, in one case, one or more identical natural periods of thestandard curve are combined to define a combined period of the standardcurve. That is, the frequency shape of each of the one or more naturalperiods is identical. As such, the length of the combined period isdivisible by any integer, in one embodiment. In another example, one ormore non-identical natural periods are combined to define a combinedperiod of the standard curve. That is, the frequency shape of each ofthe one or more natural periods is not identical. As such, the spreadamount for each natural period of the standard curve is different.Again, the length of the combined period is divisible by any integer, inone embodiment. In a concrete example, the combined period comprises twonatural periods including 8 phases. As such, the length comprises aninteger divisible by the value of eight, without remainder, since thereare 8 phases in the cycle or combined period.

In particular, as described previously, the length (l) is determined bydividing the sampling frequency by the frequency of the standard curve.As such, the length (l) can be adjusted by adjusting either or both ofthe modulation frequency (f_(m)) or the sampling frequency(f_(sampling)). For instance, the modulation frequency can be adjustedby rounding up or rounding down the target modulation frequency, inaccordance with embodiments of the present invention.

In one embodiment, the standard curve is repeatable with a shape that isrepeatable every four phases. For instance, the standard curve is anon-linear curve (e.g., a Hershey Kiss curve). The standard curve has anaverage value of zero. Examples of non-linear curves are provided inFIGS. 18A-D. As such, at 1730, the present embodiment determines alength that comprises an integer divisible by the value of four, withoutremainder, since there are four non-repeatable phases in the cycle.

In another embodiment, the standard curve is repeatable with a shapethat is repeatable every two phases. For instance, the standard curve isa linear (e.g., triangular) curve. The standard curve has an averagevalue of zero. As such, at 1730, the present embodiment determines alength that comprises an integer divisible by the value of two, withoutremainder, since there are two repeatable phases in a cycle.

Spread Spectrum Frequency Synthesizer with Improved Frequency Shape byAdjusting a Shape of a Standard Signal Used for Spread SpectrumModulation

Accordingly, embodiments of the present invention provide for thegeneration of improved frequency profiles by adjusting the shape of astandard curve when performing spread spectrum modulation.

FIGS. 19A, 19B, 19C, 20A, and 20B in combination with the previouslydiscussed figures, and in particular, FIGS. 1A, 1B, 1C, 2, 3A, 3B, 11Aand 11B illustrate embodiments of the present invention in which astandard curve is altered in such a manner to improve the frequencyshape of the standard curve when performing spread spectrum modulation.

Referring now to FIG. 19A, a flow diagram 1900A is shown illustratingsteps in a computer implemented method for sampling a curve, inaccordance with one embodiment of the present invention. Specifically,the method of flow diagram 1900A adjusts a shape of a standard curve ina spread spectrum modulator such that critical points are captured whensampling the standard curve, in accordance with one embodiment of thepresent invention. The standard curve is adjusted such that criticalpoints (peaks, zero-cross-over points, etc.) of the standard curve arecaptured when sampling the standard curve, in accordance with oneembodiment of the present invention.

Previously, in some methods, some lengths that are associated with thestandard curve can result in poor sampling of the standard curve. Thisis especially true when the modulation frequency of the standard curveis predetermined and substantially unvarying by design. For example, amodulation frequency is required to be 31.5 kHz by one manufacture. Assuch, with a pre-selected modulation frequency and a constant samplingfrequency, the associated length defining sampled points is alsorelatively constant.

For example, as previously discussed, FIGS. 18B, 18C, and 18D eachillustrate the poor sampling of the standard curve for various lengths.In particular, for a particular modulation frequency, the sample rate ofthe standard curve may not capture peaks and zero-cross-over points ofthe standard curve. In a concrete example, a frequency profile of thestandard curve can be associated with a standard length of 23 of FIG.18D. That is, for a given target modulation frequency, the standardlength over a cycle of the standard curve is equal to 23. However, asshown in 18D, improper sampling of the standard curve occurs with atarget modulation frequency that gives a length of 23. In particular,critical points at the peaks of the standard curve may be missed whensampling the standard curve. For instance, isolation areas 1844 and 1846show peaks of the ideal standard curve 1840 which are not captured whensampling the ideal standard curve 1840. This results in poor-shaping ofthe ideal standard curve and poor performance of EMI reduction.

However, in embodiments of the present invention, by altering thefrequency shape (e.g., slopes, periods, and correspondingly frequencies)within at least one cycle of the standard curve, critical points arecaptured when sampling the standard curve.

At 1910, the present embodiment generates a standard curve. In oneembodiment, the standard curve is determined by software from afunction. The software generates values representing the standard curvefor inclusion into a look-up table, for example. In another embodiment,the standard curve is generated by hardware. That is, valuesrepresenting the standard curve are determined through combinationallogic for inclusion. For instance, FIGS. 11A, 11B, 12A, 12B, 13A, 13B,13C, 13D, 14, and 15 and their corresponding discussions provide meansfor generating the standard curve. The standard curve is associated witha frequency or period defining a shape of the standard curve. Thisfrequency or period becomes a modulation frequency or period whenmodulating the VCO frequency. The standard curve is used for modulatingan input signal to generate a spread spectrum of frequencies. In oneembodiment, the unaltered standard curve is repeatable with a shape thatis repeatable every four phases of equal length, in a four phase cycleor period of the standard curve. For instance, the standard curve is anon-linear curve (e.g., a Hershey Kiss curve). In another embodiment,the standard curve is repeatable with a shape that is repeatable everytwo phases of equal length, in a period of the standard curve. Forinstance, the standard curve is a linear (e.g., triangular) curve. Instill other embodiments, the standard curve comprises a non-repeatableand non-linear curve. In other embodiments, the standard curve has anaverage value of zero.

The standard curve is analogous to the input modulation signal MS305 inFIG. 3B. Additionally, the standard curve is analogous to the standardcurve that is output from the accumulator 1120, and input to the spreadspectrum modulation loop 1130 of FIGS. 11A and 11B. It is appreciatedthat the input modulation signal or standard curve can have a variety ofdifferent configurations, including standard and/or non-standard schemes(e.g., patterns, curves, etc.). As such, the standard curve modulates aninput signal (e.g., input clock signal generated by the oscillator 211)to generate a spread spectrum of frequencies with reduced amplitude andspreading of bandwidth, in accordance with one embodiment of the presentinvention.

At 1920, the present embodiment samples the standard curve at a constantsampling frequency. In other words, the sampling frequency sets the rateat which the standard curve is sampled. In one embodiment, the samplingfrequency comprises a frequency of a P-counter in a PLL loop of thespread spectrum frequency modulator. Furthermore, as shown in FIGS. 11Aand 11B, the frequency of the PFD 221 is equal to the frequency of thevoltage controlled oscillator (f_(VCO)) divided by the feedback loopdivide value (also referred to as “P”) within the feedback loop divider224 of FIG. 1B.

At 1930, the present embodiment adjusts a shape of the standard curve,such that critical points of the standard curve are captured whensampling the standard curve. In particular, the shape of the standardcurve that is altered varies between at least two periods. That is, theshape of one period of the standard curve that is altered is differentthan the shape of another period of the standard curve that is altered.However, in one embodiment, the standard curve that is altered, isrepeatable over one or more cycles.

In particular, the standard curve is altered in order to capturecritical points when sampling the altered standard curve. As describedpreviously with regards to FIG. 18A, sampled points of the alteredstandard curve is defined by length. That is, the length of the samplingrate is defined by dividing the sampling frequency of the standard curveby the modulation frequency, as previously shown in Equation 1.

In particular, at least one portion of the standard curve is modifiedsuch that the length in that portion is altered. In that manner,critical points in the standard curve for that particular portion arecaptured when sampling the standard curve, in accordance with oneembodiment of the present invention. For instance, in one embodiment thestandard curve is altered by stretching or shrinking the length of thestandard curve in that portion so that peaks of the standard curve arecaptured. In another embodiment, the standard curve is altered bystretching or shrinking the length of the standard curve in that portionso that zero cross-over points of the standard curve are captured.

In accordance with one embodiment of the present invention, the averagelength is constant. That is, while the standard curve is altered tocapture critical points, the average number of sampled points of aperiod of the standard curve that is altered remains a constant over oneor more periods. As such, embodiments of the present invention providefor the proper adjustment of the shape of the standard curve in order tosample critical points.

FIG. 19B is a flow diagram 1900B illustrating a computer implementedmethod for sampling a linear curve, in accordance with one embodiment ofthe present invention. Specifically, the method of flow diagram 1900Badjusts a slope of the linear standard curve in a spread spectrummodulator, such that critical points are captured when sampling thestandard curve that this altered, in accordance with one embodiment ofthe present invention.

At 1940, the present embodiment generates a linear standard curve. Forinstance, FIGS. 11A, 11B, 12A, 12B, 13A, 13B, 13C, 13D, 14, and 15 andtheir corresponding discussions provide means for generating thestandard curve. The standard curve is associated with a standardmodulation frequency defining the shape of the standard curve. Inaddition, the standard curve is used for modulating an input signal togenerate a spread spectrum of frequencies. In the present embodiment,the standard curve is a linear standard curve. That is, the linearstandard curve (e.g., triangular) is repeatable every two phases in aperiod of the standard curve.

At 1950, the present embodiment samples the linear standard curve at aconstant sampling frequency. In other words, the sampling frequency setsthe rate at which the standard curve is sampled. In one embodiment, theoperation performed at 1950 is analogous to the operation performed at1920, and as such, the description provided in the discussion of 1920 offlow diagram 1900A is not repeated.

At 1960, the present embodiment captures at least one critical point ofthe linear standard curve that was previously uncaptured. That is, whensampling the linear standard curve, critical points of the linearstandard curve are captured. Specifically, the at least one criticalpoint is captured by adjusting a slope of the linear standard curve.More particularly, the shape of the linear standard curve varies betweenat least two periods. However, in one embodiment, the standard curvethat is altered is repeatable over one or more cycles.

In one embodiment, the at least one critical point is captured bymodifying the slope for one phase of a period of the linear standardcurve. More specifically, the shape of the standard curve is adjustedsuch that the slope for one phase of a period of the linear standardcurve is altered from the standard slope associated with the standardmodulation frequency.

In particular, any deviation of the slope, or correspondingly thefrequency, in any portion of one or more periods of the standard curveis implemented to capture critical points when sampling the standardcurve, in accordance with embodiments of the present invention.

For instance, FIG. 20B is a graph illustrating the manipulation of thestandard curve in order to improve EMI reduction. In other words, FIG.20B is a graph illustrating the proper sampling of the linear standardcurve, in accordance with one embodiment of the present invention.Specifically, the slope is adjusted in one phase of the linear standardcurve in FIG. 20B.

As shown in FIG. 20B, the horizontal axis represents an index indicatingthe sampled points of the standard curve. The vertical axis indicatesthe normalized y value of the standard curve between −1 and +1. Asdescribed before in relation to FIGS. 11A and 11B, the y value can bethe current value generated by the accumulator 1120 and forms part ofthe standard curve that is sent to the spread spectrum modulation loop1130, in accordance with one embodiment of the present invention. Assuch, the plurality of y values generates the standard curve.

As shown in FIG. 2000B, the combined frequency profiles of the standardcurve is associated with a length of twenty-three, where l=23. In otherwords, the average length of the altered standard curve is substantiallyequal to the standard length defined by dividing the standard modulationfrequency by the sampling frequency, as provided in previously describedEquation 1. That is, the standard curve is sampled at 23 points in oneperiod of the standard curve. Previously, without any adjusting of theslope of the linear standard curve, critical points re not captured.However, in embodiments of the present invention, by altering the slopeof the standard curve, critical points are captured.

In particular, the multi-phase standard curve comprises two phases inone period 2099 of the altered linear standard curve: phase P-1B andphase P-2B. Period 2099 begins at, but does not include, point 2092.Period 2099 ends at, and includes, point 2095.

Specifically, phase P-1B includes all points between points 2092 to2094, to include point 2094. Phase P-1B includes critical point, zerocross-over point 2093 and critical point, peak 2094. Phase P-1B issampled twelve times, and is associated with a length, where l=24. Thatis, phase P-1B is set to a first slope, where the length is defined byl=24. Phase P-1B is represented by the line connected by the opensquares.

Correspondingly, phase P-2B includes all points between points 2094 to2095, to include point 2095. Phase P-2B includes critical point, zerocross-over point 2096 and critical point, peak 2095. Phase -P-2B issampled eleven times, and is associated with a length, where l=22. Thatis, phase P-2B is set to a second slope, where the length is defined byl=22. Phase P-2B is represented by the line connected by the opencircles.

As shown in FIG. 20B, the critical points (e.g., peaks and zerocross-over points) of the standard curve are captured. This isaccomplished by adjusting the slope of a phase of the linear standardcurve. In addition, the average length of the standard curve that isaltered is substantially identical to the length of the standard curvethat is not altered, where l=23.

While the present embodiment of FIG. 20B describes the adjusting of aslope of a phase of a period of a standard curve, other embodiments ofthe present invention are well suited to the manipulation of the slopeof the linear standard curve in a point-by-point implementation. Thatis, the linear standard curve is modified over a portion of the linearstandard curve that is contained within one or more phases of one ormore periods. For instance, one portion in which the slope is adjustedcorresponds to a smaller subset of phase P-1B. That is, the slope ismodified within a phase P-1B of a period 2099 of the linear standardcurve. In another embodiment, another portion in which the slope isadjusted corresponds to a subset of phase P-1B and phase P-2B. That is,the slope is modified between phases of a period of the linear standardcurve, in one embodiment. Also, the slope is modified between phases ofone or more periods of the linear standard curve, in another embodiment.

In another embodiment of the present invention, the linear standardcurve is manipulated on a period-by-period basis. That is, the linearstandard curve is modified over an entire cycle of the standard curve.For instance, the slopes of one period of the altered standard curve areassociated with a first length. Also, the slopes of a second period ofthe altered standard are associated with a second length. That is theslope for a period of the linear standard curve is consistently modifiedthroughout all phases in that period, and is associated with a firstlength. Also, the slope for another period of the linear standard curveis consistently modified throughout all phases in that period, and isassociated with a second length.

FIG. 19C is a flow diagram 1900C illustrating a computer implementedmethod for sampling a non-linear curve, in accordance with oneembodiment of the present invention. Specifically, the method of flowdiagram 1900C adjusts a shape of the non-linear standard curve in aspread spectrum modulator, such that critical points are captured whensampling the standard curve that this altered, in accordance with oneembodiment of the present invention.

At 1970, the present embodiment generates a non-linear standard curve.For instance, FIGS. 11A, 11B, 12A, 12B, 13A, 13B, 13C, 13D, 14, and 15and their corresponding discussions provide means for generating astandard curve. The standard curve is associated with a standardmodulation frequency defining the shape of the standard curve. Inaddition, the standard curve is used for modulating an input signal togenerate a spread spectrum of frequencies. In the present embodiment,the standard curve is a non-linear standard curve. That is, thenon-linear standard curve (e.g., Hershey Kiss curve) is repeatable everyfour phases in a period of the standard curve.

At 1980, the present embodiment samples the non-linear standard curve ata constant sampling frequency. In other words, the sampling frequencysets the rate at which the non-linear standard curve is sampled. In oneembodiment, the operation performed at 1950 is analogous to theoperation performed at 1920, and as such, the description provided inthe discussion of 1920 of flow diagram 1900A is not repeated.

At 1990, the present embodiment captures at least one critical point ofthe non-linear standard curve that was previously uncaptured. That is,when sampling the non-linear standard curve, critical points of thenon-linear standard curve are captured. Specifically, the at least onecritical point is captured by adjusting a shape of the non-linearstandard curve. More particularly, the shape of the non-linear standardcurve varies between at least two periods. However, in one embodiment,the non-linear standard curve that is altered is repeatable over one ormore cycles.

In one embodiment, the at least one critical point is captured bymodifying the shape for one phase of a period of the non-linear standardcurve. More specifically, the shape of the non-linear standard curve isadjusted such that the shape for one phase of a period of the linearstandard curve is altered from the standard shape associated with thestandard modulation frequency. Also, the average length of one period ofthe standard curve is substantially equal to the standard length,wherein the standard length is determined by dividing the modulationfrequency of the unaltered standard curve by the sampling frequency.

In particular, any deviation of the period, or correspondingly thefrequency, in any portion of one or more periods of the standard curveis implemented to capture critical points when sampling the standardcurve, in accordance with embodiments of the present invention.

For instance, FIG. 20A is a graph illustrating the manipulation of thenon-linear standard curve in order to improve EMI reduction. In otherwords, FIG. 20A is a graph illustrating the proper sampling of thenon-linear standard curve, in accordance with one embodiment of thepresent invention. Specifically, the shape is adjusted in one phase ofthe linear standard curve in FIG. 20A.

As shown in FIG. 20A, the horizontal axis represents an index indicatingthe sampled points of the standard curve. The vertical axis indicatesthe y value of the standard curve between −1 and +1. As described beforein relation to FIGS. 11A and 11B, the y value is the current valuegenerated by the accumulator 1120 and forms part of the standard curvethat is sent to the spread spectrum modulation loop 1130, in oneembodiment. As such, the plurality of y values generates the standardcurve.

Also shown in FIG. 2000A, the combined frequency profiles of thestandard curve is associated with a length of twenty-three, where l=23.In other words, the average length of the altered non-linear standardcurve is substantially equal to the standard length, where the standardlength is defined by dividing the standard modulation frequency by thesampling frequency, as provided in previously described Equation 1. Thatis, the standard curve is sampled at 23 points in one period of thestandard curve. Previously, without any adjusting of the shape of thenon-linear standard curve, critical points re not captured. However, inembodiments of the present invention, by altering the slope of thestandard curve, critical points are captured.

In particular, the multi-phase, non-linear standard curve comprises fourphases in one period 2001 of the altered non-linear standard curve:phase P-1A, phase P-2A, phase P-3A, and phase P-4A. Period 2001 beginsat, but does not include, point 2010. Period 2001 ends at, and includes,point 2040.

Specifically, phase P-1A includes all points between points 2010 to2031, to include point 2094. Phase P-1A includes critical point, zerocross-over point 2031. Also, phase P-2A occupies the portion of thestandard curve after point 2031 up to and including critical, peak point2020. In addition, phase P-3A occupies the portion of the standard curveafter point 2020 up to and including critical, zero cross-over point2032. In each of the phases P-1A, P-2A, and P-3A, the correspondingphase is sampled six times, and is associated with a length, where l=24.That is, each of the phases P-1A, P-2A, and P-3A is set to a firstmodulation frequency, where the length is defined by l=24. Each of thephases P-1A, P-2 a, and P-3A is represented by the line connected by theopen squares.

On the other hand, Phase P-4A occupies a portion of the standard curveafter point 2032 up to and including critical, peak point 2040. Phase Dis sampled 5 times, and is associated with a length, where l=20. Thatis, Phase D is set to a second period, where L=20 over a full cycle.Phase D is represented by the line connected by the open circles.

As such, for three of the four phases (P-1A, P-2A, and P-3A) of aperiod, the standard curve is sampled at a rate where the length of thestandard curve over one period is l=24, where 6 points are sampled perphase. In the remaining phase (P-4A), the standard curve is sampled at arate of five points per phase, in order to capture at least one criticalpoint of the standard curve in that phase. In that manner, over oneperiod, the length of the standard curve that is altered issubstantially equal to the length of the unaltered standard curve, l=23.As a result, in FIG. 20A, the critical points (e.g., peaks and zerocross-over points) of the standard curve are captured. This isaccomplished by adjusting the shape of a phase of the non-linearstandard curve.

While the present embodiment of FIG. 20A describes the adjusting of ashape of a phase of a period of a non-linear standard curve, otherembodiments of the present invention are well suited to the manipulationof the shape of the non-linear standard curve in a point-by-pointimplementation. That is, the non-linear standard curve is modified overa portion of the linear standard curve that is contained within one ormore phases of one or more periods. For instance, one portion in whichthe slope is adjusted corresponds to a smaller subset of phase P-1A.That is, the shape is modified within phase P-1A of a period 2001 of thenon-linear standard curve. In another embodiment, another portion inwhich the shape is adjusted corresponds to a subset of phase P-1A andphase P-2A. That is, the shape is modified between phases of a period ofthe linear standard curve, in one embodiment. Also, the shape ismodified between phases of one or more periods of the linear standardcurve, in another embodiment.

In another embodiment of the present invention, the linear standardcurve is manipulated on a period-by-period basis. That is, thenon-linear standard curve is modified over an entire period of thestandard curve. For instance, the shapes of one period of the alteredstandard curve is associated with a first length. Also, the shapes of asecond period of the altered standard are associated with a secondlength. That is the shape for a first period of the linear standardcurve is consistently modified throughout all phases in that firstperiod, and is associated with a first length. Also, the shape for thesecond period of the non-linear standard curve is consistently modifiedthroughout all phases in that second period, and is associated with asecond length. For example, to achieve an average length oftwenty-three, where l=23, the frequency shape of three periods isassociated with a length, l=24. A fourth period has a frequency shapethat is associated with a length, l=20. As a result, the average lengthof the altered standard curve is associated with a length, l=23. Assuch, the critical points (e.g., peaks and zero cross-over points) ofthe standard curve are captured by adjusting the shape of a phase of thenon-linear standard curve.

Spread Spectrum Modulation with Non-Consequitive Feedback Divide Values

In a spread spectrum modulated PLL, the number of different P's used bythe P counter is often limited by the hardware. In one embodiment, afrequency modulated PLL is limited to use of four different P's. The Pvalues can be P=50, 51, 52 and 53 in one implementation and P=60, 61, 62and 63 in another implementation. It is appreciated that the values canbe different and the values 50 though 53 and 60 through 63 are justexamples. The different P values are sorted and arranged in ascendantorder in the present example. With four different P values, a P sequencelike 52, 51, 52, 50, 52, 53, 53, 52, 52, 51, . . . can be used tomodulate the PLL frequency. In one embodiment with a limited number ofdifferent P's, the frequency spread percentage is limited. For example,with P=50, 51, 52 and 53 and one frequency configuration, the spreadpercentage can only be no more than 5%.

Non-consecutive P values (or P value spread) can be utilized to increasefrequency spread in accordance with one embodiment of the presentinvention. In one embodiment, non-consecutive P values, arranged inascendant order, have a P value step larger than minimum divider stepbetween two adjacent P values. In other words, at least one spreadbetween the P values are larger than minimum spread decided by the Pcounter. For example, the minimum step of an integer divider is one asseem in P=50, 51, 52 and 53. With spread adjustment or manipulation Pvalues with a step of two or larger is non-consecutive, for exampleP=50, 52, 54 and 56. For another example, the minimum step of a halfinteger divider is 0.5. P values with a step of 1 or 1.5 isnon-consecutive. The differences between two adjacent numbers can be thesame or vary. For example, P values can increase by 3 (e.g., 50, 53, 56,59) or can vary (e.g., 50, 52, 57, 58). In this patent application, whenreferring to consecutive or non-consecutive P, it means the relationshipof different P values said above. Similar concept is also used foroffset P value PO or index of control value.

In one embodiment, a non-consecutive P value is directly used ingenerating a P sequence. In one embodiment, the P sequence generation isimplemented in software. In another embodiment, the P sequencegeneration is implemented in hardware, for example, using exemplarymodulator architectures shown in FIGS. 3A, 3B and 5B.

In one embodiment, a P sequence is generated indirectly by adjusting aninitial P sequence to a different P value spread. In one exemplaryimplementation, adjustments or manipulations are made to sorted uniquevalues associated with a control pattern. It is appreciated the sortedunique values associated with a control pattern can include an index, Pvalue or P offset value.

In one embodiment, first an initial P sequence using consecutive Pvalues is generated. For example, it can be generated by exemplarymodulator architecture shown in FIGS. 3A, 3B and 5B. Then theconsecutive P value spread can be adjusted to non-consecutive P values.For example, a consecutive P value spread of P=50, 51, 52 and 53 can bemapped to a non-consecutive P value spread of P=50, 52, 54 and 56. Inone exemplary implementation a consecutive P sequence is 52, 51, 52, 50,52, 53, 53, 52, 52, 51, . . . , is adjusted to a non-consecutive Psequence of 54, 52, 54, 50, 54, 56, 56, 54, 54, 52, . . . . In oneembodiment the P value spread adjustment is left side aligned, where themost left P values in the spread are the same. There can be right sideand center aligned adjustment too.

It is appreciated that spread adjustments in accordance with the presentinvention can operate on a variety of elements associated with P countercontrol patterns. For example, the element can be an index (e.g.i_(best) in FIG. 5B an offset P value, the P value itself, etc. In oneembodiment, the adjustment includes mapping between two sets of numbers.In another embodiment, the adjustment includes a binary number shiftingoperation to an index or offset P. In another embodiment, the adjustmentincludes arithmetic manipulation of an index or offset P value.

The FIG. 21A is a block diagram of exemplary phase lock loop controller2100 in accordance with one embodiment of the present invention. Phaselock loop controller 2100 is similar to phase lock loop controller 290except phase lock loop interface 2110 includes spread adjustmentcomponent 2111. Phase lock loop controller 2110 can be configured toimplement control indications compatible with a spread spectrum controlscheme. Phase lock loop controller 2100 includes divider controllerinterface 2110 and spread spectrum frequency control pattern generationcomponent 2130. Divider controller interface 2110 is coupled tomodulation control pattern generation component 2130.

The components of phase lock loop controller 2100 cooperatively operateto perform phase lock loop control. In one embodiment, modulationcontrol pattern generation component 2130 generates a spread spectrumfrequency modulated control pattern. In one exemplary implementation,modulation control pattern generation component 2130 is similar tomodulation control pattern generation component 300. In one exemplaryimplementation, the feedback loop divider control value is adjustablebetween consecutive and non-consecutive. The spread adjusting component2111 is controlled by non-consecutive indication signal 2109.

FIG. 21C is a block diagram of exemplary feedback loop divider controlvalues in accordance with one embodiment of the present invention.Divider indication spread 2130 has a spread of 1 between the values of2131, 2132, 2133 and 2134. Divider indication spread 2140 has a spreadof 2 between the values of 2141, 2143, 2145 and 2147. Divider indicationspread 2170 has a spread of 4 between the values of 2181, 2185, 2189 and2193. The spread is the difference between two adjacent sorted uniquenumbers.

It is appreciated that spread adjusting component 2111 can adjust thespread in accordance with a variety of adjustment schemes. In oneembodiment, spread adjusting component adjusts corresponding feedbackloop divider control values or indexes based upon a predeterminedrelationship to a difference in consecutive feedback loop dividercontrol values. In one exemplary implementation, the adjustments can bea multiple of an integer value. For example if a non-consecutive valueis twice the difference of corresponding consecutive values or amultiple of 2 the values can increase from 50, 51, 52, 53 to 50, 52, 54,56. In one embodiment the integer divider control value sequence isproduced by a non-consecutive integer spread and a half integer dividercontrol value sequence is produced by a consecutive integer spread. Inone embodiment, the spread adjusting component 2111 is a shifter thatshifts the P index or PO value to the left by 0, 1, 2 or 3 bitscontrolled by a 2-bit spread selection signal.

FIG. 21B is a flow chart of feedback loop divider control valueadjustment method 2150 in accordance with one embodiment of the presentinvention. Feedback loop divider control value adjustment method 2150permits a modulation spread amount to be increased or decreased. In oneembodiment, non-consecutive feedback loop divider control values aregenerated for an integer divider (e.g., 50, 52, 54, 56) and a halfinteger divider (e.g., 50, 51, 52, 53).

In step 2151 an initial feedback loop divider control value associatedwith a first set is generated. In one embodiment, the initial feedbackloop divider control value is generated by a modulation control patterngeneration component (e.g., 2130).

In step 2152 a spread selection signal is received. The spread selectionsignal indicates a spread pattern. In one embodiment the spreadselection signal can be utilized to indicate a non-consecutive spread.

In step 2153 the initial feedback loop divider control value is adjustedin accordance with said spread selection signal to create a new feedbackloop divider control value associated with a second set, wherein thesecond set has a different spread than the first set of block 2151. Inone embodiment, the adjustment utilizes a look-up table to map a P valueassociated with a first set of P values to another P value associatedwith a second set of P values that has a different spread. In oneembodiment, the adjustment includes shifting a binary expression of anindex value by a predetermined number of bits to the left.

A Simplified Phase Lock Loop Control Model System and Method

In one embodiment, a modulation control pattern generation component(e.g., modulation control pattern generation component 293) generatesfeedback divider control values, wherein a contribution of each of thefeedback divider control values is proportional to the difference fromeach of the feedback divider control values to an average of thefeedback divider control values. In one exemplary implementation, thecontribution of each feedback divider control value in a simplified PLLmodulation control model is governed by the relationship:contribution∝(P− P)where P is the average P value. It is appreciated that the simplifiedmodel can be readily adapted to a variety of different implementationsgoverned by a variety of simplified relationship expressions.

In one embodiment, the proportion is equal to a new feedback dividercontrol value minus an average feedback divider control value divided bythe average feedback divider control value. The contribution of eachfeedback divider control value in the simplified PLL modulation controlmodel is governed by the relationship expressed as:

${contribution} \propto \frac{P - \overset{\_}{P}}{\overset{\_}{P}}$Specifically, for the exemplary modulator architecture shown in FIGS.3A, 3B and 5B, the modulation control value is a scaled “phase error” or“error”. It is governed by expression:error=error+Δerrorwhere

${\Delta\;{error}} = {\frac{P - \overset{\_}{P}}{\overset{\_}{P}}\;{normolized\_ unit}{\_ error}}$orΔerror=(P− P )·unit_error,where the normalized_unit_error is an error contribution of an unit P(integer “one”) normalized to average P; the unit_error is the errorcontribution of an unit P (integer one), which is actually vectorresolution used in many previous examples.

In another embodiment, the control quantity is VCO frequency, and it isgoverned by expression:f _(VCO) =f _(VCO) +Δf _(VCO)where

${\Delta\; f_{VCO}} = {\frac{P - \overset{\_}{P}}{\overset{\_}{P}}\mspace{11mu}\overset{\_}{f_{VCO}}}$So with the simple PLL model, many expressions can be derived. They canbe utilized to generate spread spectrum modulation patterns forfrequency synthesizers. This can be implemented by hardware or software.

In one exemplary implementation, each feedback divider control value isassociated with a contribution to the VCO phase error. In eachmodulation step P is selected so that its contribution changes the VCOphase error to the desired value. In one embodiment similar to FIGS. 3Band 5B, an integer vector contribution v_(i) (i=1, 2, 3, . . . , n) andscaled phase error e can be used for easy hardware implementation. Inone exemplary implementation, frequency control pattern generationsystem 300 uses an integer vector contribution v_(i) and scaled phaseerror e to generate a spread spectrum modulation pattern for a frequencysynthesizer. In each step, a best P is selected so that its contributionchanges the VCO phase error to a desired value directed at reaching agoal or objective.

It is appreciated that embodiments operating in accordance with thesimplified model can cause a VCO to track a variety of patterns. Forexample, the VCO frequency can track a Hershey Kiss curve, trianglecurve, etc. It is also appreciated that the present model can beimplemented with delta sigma enhancements, high order delta sigmaenhancements, noise shaping, etc.

FIG. 22 is a flow chart of a simplified spread spectrum modulationpattern generation method 2200 in accordance with one embodiment of thepresent invention. In one embodiment, simplified spread spectrummodulation pattern generation method 2200 is similar to exemplaryfrequency spreading control patter generation method 400. In oneembodiment, simplified spread spectrum modulation pattern generationmethod 2200 is implemented in software instructions stored a computerreadable medium, where said instructions can be executed by a processorin a computer system.

In step 2210, a modulation control value is received. It is appreciatedthe modulation control value can have a variety of implementations. Forexample, a modulation control value can be a P value, a P offset, afrequency, a scaled error, etc.

In step 2200, the modulation control value is adjusted so that themodulation control value contribution is proportional to the differencebetween a feedback divider control value to an average of feedbackdivider control values. The proportion can also be defined by differencefrom each of the feedback divider control values to an average of thefeedback divider control values divided by the average of feedbackdivider control values. In one embodiment, a best feedback dividercontrol value is selected so that a VCO phase error is altered towards atarget value.

It is appreciated the simplified feedback loop divider control valueadjustment method can be implemented in software, hardware, firmware,etc. and/or a combination thereof. In one embodiment a computer readablemedium stores instructions for directing a processor to implement asimplified feedback loop divider control value adjustment method (e.g.,simplified spread spectrum modulation pattern generation method 2200).

It is appreciated that feedback loop divider control value modulationfacilitates adjustment in frequency spread percentage. In one exemplaryimplementation, the frequency spread percentage can be increased from 3%to 5%. In one embodiment a spread spectrum modulation curve envelope(e.g., a Hershey curve) can be increased with minimal distortion.

Accordingly, embodiments of the present invention provide for thegeneration of improved frequency profiles by adjusting the modulationfrequency or target frequency profile when performing spread spectrummodulation. Embodiments of the present invention provide the aboveaccomplishments and provide for a method and system for modulating astandard signal implemented within a spread spectrum frequencysynthesizer such that peaks of the standard curve are captured forimproved EMI reduction. Embodiments of the present invention provide theabove accomplishments and further provide for the generation of betterfrequency shapes for a spread spectrum modulation frequency synthesizer.Other embodiments provide the above accomplishments and are capable ofimproving the frequency shapes at peaks and valleys of a standard curvein order to improve EMI reduction, wherein the standard curve is usedfor modulation in the spread spectrum modulation frequency synthesizer.It is appreciated that the present invention can be implemented tofacilitate generation of modulated signals that are compatible with avariety of difference modulation schemes. In one embodiment, presentinvention modulation is utilized in frequency synthesis. It is alsoappreciated that the present invention can be compatible withfacilitating realization of a number of objectives, including EMIreduction, encryption, radio communication, etcetera.

The foregoing descriptions of specific embodiments of the presentinvention, a method and system for the generation of improved frequencyprofiles by adjusting the modulation frequency or target frequencyprofile when performing spread spectrum modulation, have been presentedfor purposes of illustration and description. They are not intended tobe exhaustive or to limit the invention to the precise forms disclosed,and obviously many modifications and variations are possible in light ofthe above teaching. The embodiments were chosen and described in orderto best explain the principles of the invention and its practicalapplication, to thereby enable others skilled in the art to best utilizethe invention and various embodiments with various modifications aresuited to the particular use contemplated. It is intended that the scopeof the invention be defined by the claims appended hereto and theirequivalents.

1. A method for sampling a curve, comprising: generating a standardcurve comprising a standard modulation frequency for modulating an inputsignal to generate a spread spectrum of frequencies; sampling saidstandard curve at a constant sampling frequency; adjusting a shape ofsaid standard curve, wherein at least one critical point of saidstandard curve is captured, that was previously uncaptured, whensampling said standard curve, wherein said shape of said standard curvethat is altered varies between at least two periods.
 2. The method ofclaim 1, wherein said adjusting a shape comprises: modifying saidstandard modulation frequency for a phase of a period of said standardcurve.
 3. The method of claim 1, wherein said adjusting a shapecomprises: modifying said standard modulation frequency between phasesof a period of said standard curve.
 4. The method of claim 1, whereinsaid adjusting a shape comprises: modifying said standard modulationfrequency within a phase of a period of said standard curve.
 5. Themethod of claim 1, wherein said adjusting a shape comprises: modifyingsaid standard modulation frequency for a period of said standard curve.6. The method of claim 1, wherein said standard curve comprises a lengthand further comprising defining said length by dividing a modulationfrequency of said standard curve by said sampling frequency.
 7. Themethod of claim 1, wherein said adjusting a shape comprises: modifying aslope of said standard modulation frequency, wherein said standard curvecomprises a linear standard curve.
 8. The method of claim 1, whereinsaid adjusting a shape comprises: adjusting said shape of said standardcurve such that an average length associated with said standard curve isconstant.
 9. The method of claim 1, wherein said sampling said standardcurve comprises: sampling said standard curve at said samplingfrequency, wherein said sampling frequency comprises a frequency of aphase frequency detector.
 10. A method for sampling a curve, comprising:generating a linear standard curve comprising a standard modulationfrequency for modulating an input signal to generate a spread spectrumof frequencies; sampling said linear standard curve at a constantsampling frequency; capturing at least one critical point of said linearstandard curve, that was previously uncaptured, when sampling saidlinear standard curve by adjusting a slope of said linear standardcurve, wherein a shape of said linear standard curve that is alteredvaries between at least two periods.
 11. The method of claim 10, whereinsaid capturing a critical point comprises: modifying said slope for onephase of a period of said linear standard curve.
 12. The method of claim10, wherein said capturing at least one critical point comprises:modifying said slope between phases of a period of said linear standardcurve.
 13. The method of claim 10, wherein said capturing at least onecritical point comprises: modifying said slope within a phase of aperiod of said linear standard curve.
 14. The method of claim 10,wherein said capturing at least one critical point comprises: modifyingsaid slope for a period of said linear standard curve.
 15. The method ofclaim 10, wherein said capturing at least one critical point comprises:modifying said slope such that an average length associated with saidstandard curve is constant.
 16. A method for sampling a curve,comprising: generating a non-linear standard curve comprising a standardmodulation frequency for modulating an input signal to generate a spreadspectrum of frequencies; sampling said non-linear standard curve at aconstant sampling frequency; capturing at least one critical point ofsaid non-linear standard curve, that was previously uncaptured, whensampling said non-linear standard curve by adjusting a shape of saidnon-linear standard curve, wherein said shape of said non-linearstandard curve that is altered varies between at least two periods. 17.The method of claim 16, wherein said capturing at least one criticalpoint comprises: modifying said standard modulation frequency for oneperiod of a period of said non-linear standard curve.
 18. The method ofclaim 16, wherein said capturing at least one critical point comprises:modifying said standard modulation frequency between phases of a periodof said non-linear standard curve.
 19. The method of claim 16, whereinsaid capturing at least one critical point comprises: modifying saidstandard modulation frequency within a phase of a period of saidnon-linear standard curve.
 20. The method of claim 16, wherein saidcapturing at least one critical point comprises: modifying said standardmodulation frequency for a period of said non-linear standard curve.